National Seminar on Ferroelectrics and Dielectrics

(NSFD-XIII)

 

 

 

 

Department of Physics and Astrophysics

 University of Delhi, Delhi-110007, India

 

 

 

 

 

 

 

 

 

 

         CONTENTS

 

SESSION                                            ABSTARCTS                         PAGE

                                                                                               

 

I       PLENARY SESSION                                 (K-01,  I-01, I-02)

 

 

II       SYNTHESIS OF NOVEL                         (I-03 to I-05)

            MATERIALS                                            (PA-01 to PA-08)

 

 

IIIA   RELAXORS & FERROICS    (I-06A to  I-08A)

                                                                                (O-04A to O-06A)

                                                                                (PA-09 to PA-21)

 

IIIB  CRITICAL ISSUES IN                              (I-06B  to  I-08B)

          FERROELECTRICS                 (O-04B to O-06B)

                                                                                (PA-22 to PA-28)

 

 

IV       PROCESSING AND                                (I-09 TO I-11)

           CHARACTERIZATION –I     (O-07 to O-09)

                                                                                (PA-29 to PA-45)

 

V        PIEZOELECTRIC AND                          (I-12 , I-13)

           PYROELECTRIC                     (O-10 to O-12)

                                                                                (PB-01 to PB-09)

 

VI A    THIN FILMS - PROCESSING              (I-14A  to  I-16A)

             AND STUDIES                                        (O-13A to O-15A)

                                                                                (PB-10 to PB-24)

 

VI B      PROCESSING AND                             (I-15B  to  I-16B)

              CHARACTERIZATION-II   (O-01 to O-03)

                                                                                (O-13B to O-15B)

                                                                                (PB-25 to PB-45)

 

VII        DIELECTRICS AND                             (I-17 TO I-19)

              RELAXATION MECHANISM    (O-16 to O-18)

                                                                                (PC-01 to PC-23)

 

VIII      OTHER RELATED TOPICS                (I-20 , I-21)

                                                                                (O-19 to O-21)

                                                                                (PC-24 to PC-43)

 

 

 

 

 

 

 

 

SESSION I

PLENARY SESSION

Tuesday, November 23, 2004

11.15 A.M.   -    01.15 P.M.

 

 

K-01

 

R&D WORK FOR QUARTER CENTURY IN FERROELECTRICS AND OTHER OXIDE MATERIALS

 

M. S. Multani,

 

Dept. of condensed Matter Physics and Materials Science

Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005

 

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I-01                                                                                                17

 

EMP AND SIMULATION RESEARCH ON

MICROWAVE DIELECTRICS

 

Hsiu-Fung Cheng¹, Yi-Chun Chen², and I-Nan Lin³

 

¹ Dept. of Physics, National Taiwan Normal Univ., Taipei 116, Taiwan, R. O. C.

² Dept. of Physics, National Cheng Kung Univ., Tainan 701, Taiwan, R. O. C.

³ Department of Physics, Tamkang Univ., Tamsui 250, Taiwan, R. O. C.

 

Recent EMP and simulation studies on the dielectric properties of microwave materials are necessary due to the rapid development of photonics, electro-optical industry and electromagnetic wave communication. A novel evanescent microwave probe (EMP) combined with systematically quantitative analyses is introduced in this study. The EMP measurement is based on the scanning-probe and the near-field techniques. Briefly, the system design consists of a sharp metal tip protruding through the endwall of a coaxial resonant cavity. The high spatial frequency components of evanescent waves generated at the tip are inversely proportional to tip radius and currently reach l/10⁵ on dielectric samples. However, due to the complexity of the near field distribution in the tip-sample region, it is difficult to obtain an analytical solution of the sample properties. To overcome this problem, we use a 3-dimensional (3D) finite element simulation and equivalent circuit to model the behavior of the electromagnetic field inside the resonant cavity and near the tip. A modified analysis on sample quality factor, which is usually dominated by conductor losses of the resonator, is especially proposed. Experimental results on various dielectric samples are also obtained to support the theoretical ones, which demonstrate that the analyses are useful for EMP investigation, and provide a way for surface dielectric imaging. In addition, the dielectric characteristics such as relative permittivity & dielectric losses can be determined along with surface dielectric imaging in EMP and simulation studies.

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I-02                                                                                                29

                         

RARE EARTH SUBSTITUTED Bi₄Ti₃O₁₂ THIN FILMS

AND FERROELECTRIC RESPONSE

 

M.S. Tomar

 

Physics Department, University of Puerto Rico,

Mayaguez, PR 00681-9016,

mtomar@uprm.edu

 

Rare earth substituted elctroceramic bismuth titanate has emerge as new material system for non-volatile ferroelectric memory devices [1, 2].  Rare earth substituted Bi₄Ti₃O₁₂ thin film structures for various compositions were deposited on Pt (Pt/TiO₂/SiO₂/Si) substrate.  Study of the leakage current is important in these devices because it affects the saturation, fatigue and reliability. Temperature dependent leakage current, fatigue, and ferroelectric response were investigated on Pt/film/Pt capacitor structures.  Large ferroelectric polarization (P_r) values of 50 to 70 μC/cm² and leakage current I < 10^-10A were observed.  The possible explanation of the large polarization and an overall assessment of the current state of technology will be discussed.  Low leakage current and giant ferroelectric response indicates that this material system could replace the current PZT and BST based devices.

Reference

1. M.S. Tomar, R.E. Melgarejo, A. Hidalgo, S.B. Mazumdar, R.S. Katiyar, Appl. Phys. Lett. 83, 341 (2003)
2. R.E. Melgarejo, M.S. Tomar, S. Bhaskar, P.S. Dobal, R.S. Katiyar, Appl. Phys. Lett. 81, 2611 (2002)

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SESSION II

SYNTHESIS OF NOVEL MATERIALS

Tuesday, November 23, 2004

02.00 P.M.   -    03.30 P.M.

 

I-03                                                                                                 11  

LOW SUBSTRATE TEMPERATURE DEPOSITION OF

Pb(Zr,Ti)O₃ THIN FILMS BY USING Ba(Mg_1/3Ta_2/3)O₃

AS BUFFER LAYER

 

I-Nan Lin^1,2*, Hsiu-Fung Cheng³  and Ying-Hao Chu⁴

 

¹Dept. of Physics, Tamkang University, Tamsui, Taiwan 251, R.O.C.;

²Materials Sc. Center, National Tsing Hua Univ., Hsin Chu, Taiwan 300, R.O.C.;

³ Dept. of Physics, National Taiwan Normal Univ., Taipei, Taiwan 116, R.O.C.

⁴Dept.of Materials Sc.& Engg, National Tsing Hua Univ., Hsin-Chu, Taiwan 300.

* inanlin@mail.tku.edu.tw & inlin@alumni.nthu.edu.tw

 

Pb(Zr_1-xTi_x)O₃, PZT, thin films possess marvelous ferroelectric properties and have attracted much attention for application in nonvolatile ferroelectric random access memory (FeRAM). However, directly growth of PZT on silicon-based substrates is very difficult as the PZT materials interact with substrate materials seriously, which degrades the ferroelectric properties of the PZT films.. Recently, we attempted to use a new buffer layer, Ba(Mg_1/3Ta_2/3)O₃, BMT, to suppress the PZT-to-Si interdiffusion and, at the same time, to enhance the nucleation of PZT crystalline phase. How the growth behavior BMT buffer layer influences the formation kinetics of PZT films was investigated. It was observed that through the utilization of BMT buffer layer, pure perovskite PZT thin films could be obtained on bare or platinum-coated silicon substrates by in-situ pulsed laser deposition (PLD) process at 350. Forming a continuous BMT layer is of critical importance to grow PZT films at such a low substrate temperature. The low temperature deposited PZT films possess superior dielectric and ferroelectric properties, viz. they exhibit high dielectric strength with large memory window (W_M=4.2 V), when deposited on bare Si-substrates, and show good ferroelectric properties (P_r=29.9 μC/cm², Ec=118 kV/cm, fatigue properties >10¹¹ cycles), when deposited on Pt(Si)-substrates.

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I-04                                                                                               153

FERROELECTRIC SUPERLATTICES

 

S.B. Krupanidhi

 

Materials Research Centre, Indian Institute of Science, Bangalore-560012.

 

The limitations of conventional high dielectric materials for the fabrication of tera-level devices and their device performance can be overcome by the fabrication of a new conceptual material selection, and design of artificial lattice materials based upon the growth of monoatomic layer unit lattice thicknesses.  Ferroelectric superlattices have been recently studied to obtain articulated functionality or enhanced properties over single homogeneous layer oxide thin films.  Therefore extensive research has been carried out to obtain large dielectric constant and nonlinear dielectric properties since the dielectric properties are of fundamental importance in electrically tunable microwave devices.  The other application includes tera bit level semiconductor electronic devices such as high k capacitors and gate dielectrics.

Several ferroelectric material compositions are available to explore these possibilities, while Ba and Pb based Perovskites received maximum attention.  Present work involved the development of superlattice structures using PLD (Pulsed laser deposition) in a combinatorial mode.

The present talk deals with the implementation of innovative approach to understand the superlattice growth, surface and interface processes and their dielectric behavior.

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I-05                                                                                              192        

COMPETING INSTABILITIES AND

FRUSTRATION IN (Sr_1-xCa_x) TiO₃

 

Dhananjai Pandey

School of Materials Science and technology, Institute of Technology

Banaras Hindu University, Varanasi-221005

 

The purpose of this talk is to provide an overview of various phase transitions in the (Sr_1-xCa_x)TiO₃ system driven by zone center and zone boundary soft modes. One of the end members of this system, SrTiO₃, is a well-known quantum paraelectric with incipient ferroelectric behaviour. Recently, we have shown that the other end member i.e. CaTiO₃, is an incipient antiferroelectric. Ca⁺² doping at the Sr⁺² site above a critical concentration (x_c =0.0018) stabilizes X-Y type quantum ferroelectricity. With increasing Ca⁺² content, the variation of dielectric constant with temperature reveals a diffuse transition up to x = 0.12. This diffuseness has recently been explained by us in terms of frustration caused by competing ferroelectric and antiferroelectric instabilities. The discovery of an antiferroelectric phase transition for x>0.12 and the presence of both ferroelectric and antiferroelectric Raman modes for x=0.12 provide direct support to the frustration model for compositions with x £ 0.12. Results of XRD, neutron diffraction, Raman scattering and dielectric studies will be presented in this talk to elucidate the rich variety of phase transitions in this mixed perovskite system.

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PA-01                                                                                              30

STRUCTURAL AND MAGNETIC BEHAVIOR

OF Zn_1-XCo_XFe₂O₄ FOR SPINTRONICS

 

M.S. Tomar, R.P.Guzman, R.E. Melgarejo, S.P. Singh

 

Physics Department, University of Puerto Rico, Mayaguez, PR 00681-9016

 

Several magnetic element doped oxide materials are important for spintronic applications. Some of them have shown week ferromagnetism at room temperatures.  CoFe₂O₄ is a well known ferrite with well defined ferromagnetic response.  It is expected that the partial replacement of Co by Zn may affect the magnetic properties, and this material may be useful for spin injection ZnO/CoFe₂O₄ devices. We report on the synthesis of Zn_1-xCo_xFe₂O₄ by solution chemistry route. The structural and ferromagnetic properties were investigated using X-ray diffraction, Raman spectroscopy and SQUID.  X-ray diffraction patterns and Raman spectroscopic studies indicates mixed phase material for higher Co concentration. Zn_1-xCo_xFe₂O₄ with compositions with low concentration of Zn shows interesting magnetic behavior as indicated by SQUID measurements. Details of the material processing and SQUID measurements will be presented.

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PA-02                                                                                             27

MAGNETOELECTRIC PROPERTIES IN LAMINATED COMPOSITES OF PIEZOELECTRIC AND

MAGNETOSTRICTIVE OXIDES

 

S. Narendra Babu*, T.Bhima Sankaram and S.V.Suryanarayana

Materials Research Lab., Dept.of Physics, Osmania Univ., Hyderabad-500007

narendra_sim@yahoo.co.in

 

In two- phase composites consisting of Piezoelectric and Piezomagnetic materials, under the action of an external magnetic field, Magnetoelectric (ME) output results, which is absent in either of the phases.  In the present work, the laminates of Ni-Co-Mn ferrite (NCF) and Lead Zirconate Titanate (PZT) were prepared. Magnetoelectric (ME) output of these laminates are investigated. The geometry of the samples is NCF-PZT-NCF. Thickness of NCF varied between 0.5 to 1mm.  Thickness of PZT varied between 0.3 to 1mm.  With increasing the thickness ratio the ME output increases.  The highest ME output of 3536 mV/cm is found to observed at a fixed AC magnetic field of 64 Oe and 1.008 KHz AC frequency for the sample with thickness of NCF 1mm and thickness of PZT 0.3mm.  The Magnetoelectric coefficient (a) is calculated.   

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PA-03                                                                                              77

NANOFERROELECTRIC MATERIALS BY

MECHANICAL ALLOYING

 

S. K. S. Parashar, R. N. P. Choudhary and B. S. Murty*

Department of Physics and Meteorology, I.I.T, Kharagpur, 721302

*Dept. of Metallurgical & Materials Engineering, I.I.T. Madras, Chennai-60003

sksparashar@yahoo.com

 

The properties of nanocrystalline materials are found superior to those of conventional polycrystalline coarse-grained materials. Though nanocrystalline ceramics can be synthesized by different physical, chemical and mechanical methods Mechanical alloying (MA) offers several advantages over the other methods. Nanoceramic/alloys prepared by MA can exhibit exceptionally high diffusivity, and sinterbility, and unusual formability in conventionally brittle materials at ambient temperature. Nanoferroelectrics rare-earth modified PZT (PRZT where R= Nd, and Gd) has been synthesized by a novel mechanical alloying technique. In order to have a better understanding of the phase transition, relaxation time with smaller particle size, we have synthesized exceptionally high dielectric constant nanocrystalline ferroelectrics on which not much work have been reported so far. X-ray diffraction (XRD) studies shows that these compound has new cubic phase in milled condition and tetragonal on annealing. Detailed studies of dielectric properties of PRZT as a function of temperature shows that Tc, decreases with the decrease in crystallite size and diffusivity increases with increase in milling time.

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PA-04                                                                                               95

DIELECTRIC PROPERTY OF NANOCRYSTALLINE CdS PARTICLES GROWN IN A POLYMER MATRIX

BY CHEMICAL BATH DEPOSITION

 

P.K. Ghosh, Sk.F. Ahmed and K.K. Chattopadhyay*

 

Dept. of Physics, Thin Film & Nano Science Lab, Jadavpur Univ.,Kolkata 700 032

kkc@juphys.ernet.in

 

The unconventional properties of nanostructured materials have recently attracted the renewed interest because of their potential uses in both mesoscopic research and the development of nanodevices. The dielectric property exhibited by nanometer-sized materials is one of the most attractive properties for practical applications. Polymer / nanoparticles composites have been increasingly studied because of their enhanced optical and electrical properties. Recently, a method of making nanostructure by electro-chemical deposition of materials into an array of self-organized pores has been developed. We have used CBD method with which nanostructured CdS particles have been grown within the self-organized pores of polyvinyl alcohol (PVA). We have chosen the CBD method, as it is one of the most popular and wide-spread technique in the area of thin film technology, because of its many advantages such as easier composition control, better homogeneity, low processing temperature, lower cost, easier fabrication of large area films, possibility of using high purity starting materials and having an easy coating process of large and complex shaped substrates.

The variation of dielectric constant as a function of frequency for samples of CdS nanoparticles dispersed in PVA with average dispersibility (h) have been measured under vacuum (10^-3 Torr) by using an L-C-R meter. Dielectric constants of the CdS-PVA composite lies in the range 120 to 250 at high frequency which are much higher than that of only PVA having dielectric constant ~28. The large value of dielectric constant of nanocomposite (PVA / CdS) is due to the fact that the nanoparticles of CdS within PVA are disconnected from each other and under the application of voltage, these nanoparticles act as nanodipole. As the particle size is in nanometer order, the number of particles per unit volume increases, hence dipole moment per unit volume increases, so dielectric constant increases. Again, it is also observed that the dielectric constant of the films decreases with increase of dispersibility, which is expected for our films. This is due to the fact that when the dispersibility of the films increases, the inter nanoparticles separations are also increases, that means the number of nanoparticles per unit volume decreases, which implies that under application of voltages, the nanodipoles per unit volume decreases. Hence dielectric constant decreases. It has also been observed that, for each dispersibility of CdS nanoparticles in the films, the dielectric constant is almost constant at high frequency range i.e. there is no dispersion at high frequency.

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PA-05                                                                                            176

GROWTH OF LEAD TITANATE AND ZINC OXIDE NANO-RODS BY PULSED LASER DEPOSITION

 

Vinay Gupta*, P.Bhattacharya, Anju Dixit, and R.S.Katiyar

 

*Department of Physics & Astrophysics, University of Delhi, Delhi-110007

Department of physics, University of Puerto Rico, San Juan, USA.

 

Lead titanate and Zinc oxide has been considered promising materials for applications in modern nano-electronics and MEMs. Very recent demonstrations of novel devices include a nano-scale laser and the electrochemically gated quantum dot transistor. The availability of large quantities of well-aligned nanorods is extremely important and there synthesis on silicon wafer could be exploited for the integration of the existing microelectronic technology with the nanoscale functional devices. The pulsed laser deposition technique has been given rare attention for the fabrication of nanorods besides the fact that it maintains the stoichiometry, and leads to the fabrication of epitaxial and single crystalline films at relatively lower temperatures.

In the present work nano-rods of Zinc oxide (ZnO) and lead titanate (PT) were fabricated on Si substrates using pulsed laser ablation. ZnO nanorods with diameters in the range of 70-350 nm and up to 15 mm long were fabricated directly on silicon substrate at a relatively low processing temperature (450 ^oC) without using any catalytic template. The influence of substrate temperature and the oxygen pressure on the formation of ZnO nanorods was investigated. The Raman scattering studies and scanning electron microscopy results indicated that the ZnO nanorods grown on Si were well aligned along c-axis and isolated from each other. The additional Raman modes at ~ 477 cm^-1 and 574 cm^-1 were observed in the c-axis oriented ZnO nanorods which were assigned to the activation of the upper and lower surface phonon modes respectively. The layer of Platinum was used as a catalytic template for the fabrication of PT nano rods on Si. The rods were polycrystalline in nature. The successive deposition of nano-particles of these oxides one over the other at higher chamber pressure results in the formation of elongated nano-rods. The temperature dependent Raman scattering studies confirm the ferroelectric nature of fabricated PT nano-rods and the phase transition were detected from the changes in Raman peaks.

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PA-06                                                                                               99

ELECTRICAL PROPERTIES AND MAGNETOELECTRIC EFFECT IN CoFe₂O₄ + Ba_0.8Pb_0.2TiO₃ COMPOSITES

 

S.L.Kadam¹, D.R. Thube², T.S. Thopate², P.S. Mutkule², B.K. Chougule*

 

¹Physics Department, ²Chemistry Department, New Arts, Commerce & Science College,Pamer. Tal-Parner, Dist.-Ahmednagar-414302. Maharashtra, India.

*Dept. of Physics, Composites Materials Lab., Shivaji Univ., Kolhapur–416004.

 

Magnetoelectric  phenomenon has been observed in several single phase materials in which simultaneous electric and magnetic ordering co-exists and in two-phase composites in which the participating phases are ferrite and ferroelectric.  Hence, magnetoelectric composites with composition xBa_0.8Pb_0.2TiO₃ + (1-x)CoFe₂O₄ in which x varies as 0.0, 0.55,  0.70, 0.85 and 1.0 were prepared by ceramic method.  The presence of both phases was confirmed by x-ray diffraction technique.  The variation of resistivity and thermoemf of the composites with temperature was studied.  The variation of dielectric constant (e^’ ) with frequency (100 Hz to 1 MHz) and with temperature at different frequencies viz. 1 kHz, 10 kHz, 100kHz and 1 MHz has been also studied.  The ac conductivity is derived from dielectric constant (e^’) and loss tangent (tan d).  The nature of conduction has been discussed with the help of polaron hopping model.  The static value of the magnetoelectric conversion factor i.e. dc (ME)H was studied as a function of intensity of the magnetic field.

 

Keywords: Electrical properties, Polaron conduction, ME effect.

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PA-07                                                                                              177

NANO-SCALE MOLECULAR TECHNOLOGIES AND THEIR RELATIONSHIP WITH THE DYNAMISM OF SOLITONS AT

SINE-GORDAN KINK AND ANTI-KINK POINTS

 

M.M. Bajaj, S. Singh, P.K. Sethy and R. K .Jha

 

Department of Physics & Astrophysics, University of Delhi, Delhi-110007

 

 Recent progress in materials with second order linearity, including polymeric electro-optical wave guides, has stimulated experimentalists to work, design and develop devices for self guide beams (Spatial Optical Solitons) . The surface of a layer of fluid (water for instance) in motion can show a variety  of “patterns” formed by wave crests, which diminish or increase in height, disappear, propagate, collide with other crests. The solitons provide a new line in research in systems, which are wave-like in nature, e.g. systems involving fluids or light. The soliton is a quasi-particle, which consumes its character and interacts with its surroundings and other solitons as particle. The stability of solitons stems from the delicate balance of  “nonlinearity” and “dispersion”. Nonlinearity drives a solitary wave to concentrate further, whereas the dispersion is the effect to spread such a localized wave. If one of these two competing effects is lost, solitons become unstable and, eventually, cease to exist. Solitons are completely different from “linear waves” like sinusoidal waves. Instead of trying to describe complete fluid or light, we can concentrate on the evolution of solitons, which stay around in the systems forever and constitute the most important part in the dynamics. In the present work we have made an attempt to examine the mathematical aspects of devices based on solitonic dynamism.

 

Keywords : Solitons, Solitonic dynamism, Molecular electronics, Field theory, KdV equations, Sine-Gordon kink  and anti-kink.

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PA-08                                                                                                                    114

CONCENTRATION SENSITIVE ELECTRICAL AND MAGNETIC PROPERTIES OF IRON OXIDE / CONDUCTING

POLYMER NANOCOMPOSITE

 

Raksha Sharma* and S. Annapoorni

Department of Physics and Astrophysics, University of Delhi, Delhi, 110007

raksha0808@yahoo.co.uk, rsharma1@physics.du.ac.in

 

Nanocomposites of Iron oxide (g-Fe₂O₃)-conducting polymer systems exhibit interesting magnetic and electrical properties. The properties are found to depend very strongly on the iron oxide: polymer ratio. In the present investigation we report the magnetic and electrical properties of magnetic nanocomposite wherein the two conducting polymers polypyrrole (PPy) and polyaniline (PANI) are used. These organic-inorganic nanocomposites itself have very reduced agglomeration in comparison to the sol gel prepared iron oxide nanoparticles. The particle size as estimated from Transmission Electron Microscopy (TEM) is found to vary from 10 nm to 15 nm.  Chains of iron oxide particles were observed in the case of polyaniline - iron oxide nanocomposites for certain specific concentration. The XRD measurements show the presence of cubic Fe₂O₃ phase for all the compositions.  Weight loss estimated from DTA-TGA studies show that the amount of polymerization is more in the case of polyaniline as compared to polypyrrole.

Electrical conductivity measurements performed at room temperature shows large variation in conductivity with small change in polymer concentration. The high value of conductivity and agreement of conduction mechanism  with Mott’s VRH model revealed that the conduction mechanism in these nanocomposites is dominated by the conducting polymer polypyrrole.The dielectric measurement show a Debye type of relaxation process and dielectric constant show very small variation at low temperature and large variation at higher temperature. The measured value of e’ at 1 kHz, 10 kHz, 100 kHz and 1 MHz clearly show a saturation region at high temperature and this may be used as an estimate of e_o.

Hysteresis measurements were carried out in the range –15 to 15 Tesla at room temperature. The magnetic hysteresis shows reduced value of saturation magnetization in the presence of polymer. The saturation magnetization was measured to be 43.4 emu/gm and 57.8 emu/gm for iron oxide:PANI composite and iron oxide:PPy composite  respectively.  This variation in saturation magnetization is attributed to more polymerization of polyaniline in comparison to polypyrrole. The low value of coercivity indicates that the system is close to superparamagnetic behavior.

References

1.<       Lie Chen, Weng-jun Yang and Cheng-Zheng Yang, J. Mater. Sci 32, 3571 (1997)

2.<       S. Maeda and S.P.Armes, J.Mater. Chem. 4, 935 (1994)

3.<       C.L.Huang and E. Matijevic, J. Mater. Res. 10, 1327 (1995)

4.<       J. H. Dormann and D. Fiorani, Magnetic properties of fine particles, (North Holland, Amsterdam), 1992.

5.   Komilla Suri, S. Annapoorni, R.P.Tandon, J. Non Crystalline Solids 332, 279 (2003)

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SESSION III A

RELAXORS AND FERROICS

Wednesday, November 24, 2004

09.00 A.M.   -    11.00 A.M.

 

 

 

I-06A                                                                                             82        

MULTILAYER CERAMIC ACTUATOR – A VERSATILE DEVICE FOR A VARIETY OF APPLICATIONS

 

Denny P.Alappattu, G.Unnikrishnan, K.G.Vasanthakumari,

K.Sasidharan and N.Raghu*

Centre for materials for electronics technology (C-MET),

Athani P.O, M.G.Kavu, Thrissur, kerala–680771

rkg124@rediffmail.com

 

Actuators that provide precise and controlled movement are becoming essential elements in electronics and smart structures.  Ceramic actuators are far superior to conventional actuators in terms of precision, accuracy, response speed and generative force.  The need for miniaturized devices coupled with less driving power has lead to the development of multilayer actuator.  Current trend is to go in for lower and lower operating voltages (£150V) which in turn demand individual layer thickness  £100mm.  Multilayer actuators are manufactured through a cost effective but technically intense route.  Tapecasting is the backbone of multilayer process. 

This paper deals with the development of both piezoelectric actuators based on PZT and electrostrictive actuators based on PMN-PT material.  Optimization of tapecasting slurry rheology and multilayer processing is described at length for both the systems.  This paper outlines the design, development, characterization and associated reliability issuses of multilayer actuators.  The potential application of multilayer actuators in different field is also discussed.

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I-07A                                                                                            139

NEW DEVELOPMENTS IN MULTIFERROICS

 

Vaijayanti R. Palkar

Dept. of Condensed Matter Physics & Materials Sc., T.I.F.R., Mumbai 400005

 

Multiferroics are characterized by a coexistence of ferroelectric and ferromagnetic orderings. Discovery of the induction of polarization by a magnetic field and of a magnetization by an electric field created a lot of excitement in the 1960s. The cross-link between magnetic and electric properties opened new degree of freedom for device designing. However, in real life the scarcity of materials exhibiting multiferroic behavior at room temperature restricted their usage in device applications. The shortage of multiferroic materials is due to the fact that transition metal d electrons, which are essential for the presence of magnetic moment, reduce lattice distortion, which is essential for ferroelectric behavior. As a result, additional structural or electronic driving force is required for ferroelectric and magnetic ordering to occur simultaneously at room temperature. The hetero-structures of piezoelectric and magnetostrictive phases, which could be electromagnetically coupled via stress mediation, are therefore used as an alternative to create ME effect. But the structural non-compatibility and reactivity between two materials and also with the substrate, generates immense difficulties in growing hetero-structures and achieving coupling between the two order parameters.

Recently, we have been able to show that Tb doping at Bi site induces ferrimagnetism in antiferromagnetic BiFeO₃ without disturbing ferroelectric properties. We are also successful in converting ferroelectric PbTiO₃ to a compound with superior multiferroic properties. Remarkably, in this newly synthesized compounds both magnetic (T_M) and ferroelectric transitions (T_C) occur above room temperature. The observed coupling between the two order parameters is an added advantage. The present talk will cover the interesting results obtained in these novel compounds.

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I-08A                                                                                                31

STRONTIUM BARIUM NIOBATE: LEAD FREE FERROELECTRIC RELAXORS

 

A R. Kulkarni and Pankaj Patro

Dept. of Metallurgical Engg. & Materials Sc., I.I.T-Bombay, Mumbai 400076

ajit.kulkarni@iitb.ac.in

 

 

Lead free ferroelectric materials have gained attention because of environmental concerns.  Strontium Barium Niobate (SBN), is one such material which is at the forefront among the lead free ferroelectrics because of its wide applicability. However, the unusual sintering behavior of SBN leads to abnormal grain growth, duplex microstructure and low density has severely affected successful commercialization of SBN.

Here we report, synthesis of SBN with better dielectric and ferroelectric properties that are achieved through control and elimination of abnormal grain growth. Dielectric characterization was performed from room temperature to 250°C at different frequencies. SBN showed dielectric constant >2300 at room temperature and >2700 at T_m, depending on sintering temperature. Vogel-Fulcher relationship revealed the dipolar glass nature of SBN with freezing temperature T_f = ~315K. Ferroelectric measurements were carried out at room temperature as well as higher temperatures to understand the behavior of hysteresis loop at the electric field of 15KV/cm. The largest polarization was found to be 5.59 mC/cm². I-V characteristics for these materials showed a variation of leakage current from 10^-5 to 10^-11 A on increasing the applied field from zero to maximum value. Leakage current was measured at 1000ms “soaking time” and 10000ms “measured time” and found to be varying between 10^-6 to 10^-8 A. Fatigue measurement was done over 10⁶ electric cycles at 15 KV/cm. The reduction in saturation polarization in some samples was found to be only 0.06% after the electric cycling fatigue. The material is found to follow modified Neel’s law indicating the presence of non-zero interaction polarization. These properties will be compared with some of the lead based ferroelectrics to assess the potential of SBN to be used as replacement of Lead based Ferroelectrics.

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O-4A                                                                                             106

PREPARATION, STRUCTURAL CHARACTERIZATION

AND ELECTRICAL PROPERTIES OF SOME

Pb(B_1/3Nb_2/3)O₃ RELAXORS

 

Mukul Pastor, P.K.Bajpai* and R.N.P. Choudhury**        

*School of Pure & Applied Physics, Guru Ghasidas University, Bilaspur 495 009

**Department of Physics & Metrology, I.I.T., Kharagpur, West Bengal.

bajpai_pk@yahoo.com

 

Lead based relaxors find widespread industrial applications such as multilayer capacitors, electro-mechanical coupling devices and actuators due to their low temperature sinterability, high permittivity and low temperature coefficient of capacitance and excellent optical and electrostrictive properties. Pure perovskite phase are often not formed and X7R standard is very rarely met in the reported materials. It is therefore important to understand the cause of mixed phase formation and modifications required in the preparation process for single phase.

In this paper we, therefore, report the preparation, structural characterization and dielectric behaviour of some lead based materials. Two-stage columbite solid state reaction routes has been used for the preparation of Pb(B′_1/3Nb_2/3)O₃. XRD patterns are used for quantitative estimation of perovskite phase and low frequency dielectric relaxation is analyzed. Final phase materials gets stabilized in mixed phase. These are found to be mixtures of cubic pyrochlore and perovskite phase Dielectric responses at temperatures above T_m show the degree of relaxation varying in different materials. The DC electrical conductivity follows Arhenius behavior and the activation energies calculated matches quite well with those reported in similar systems.

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O-05A                                                                                            136

POTENTIAL APPLICATIONS OF PIEZOELECTRIC TRANSDUCER IN DEFENCE SECTORS

 

H. Muthururajan, H.H. Kumar and D.K. Kharat

Armament Research and Development Establishment, Pashan, Pune – 411 021

 

The most notable applications of piezoelectric transducers in defence sectors are reviewed in this paper. Research on piezoelectric materials continued throughout the early twentieth century, in part stimulated by military interests arising from World War I. A major outcome of this research was the use of piezoelectric quartz in acoustic projectors and receivers. World war II brought increased attention to the study of piezoelectric materials especially for use in radio communications and underwater acoustic applications. Extensive research and development throughout the last four decades has led to the use of piezoelectric ceramics in a wide variety of commercial, consumer and military applications ranging from inexpensive tonal buzzers used in toys to sophisticated ultrasound imaging transducers used in the latest medical procedures, from consumer fish finders to highly complex submarine sonar systems and from simple grill ignitors to all manner of force and acceleration sensors.  The discovery of the piezoelectric effect and the advent of transducers acted as a powerful stimulus, in the  underwater acoustics in submarine / anti-submarine warfare systems, IR sensor, pressure / force sensing device, detonator, ferroelectric RAM and may find applications in piezoelectric smart MEMs. An overview of piezoelectric transducers from the perspective of its potential enabling technologies in defence sectors such as piezoelectric hydrophone, highly complex submarine sonar system, actuators, detonator, microelectromechanical system (MEMs), gyroscopes etc., are presented. This paper also highlights the various piezoelectric materials developed by our establishment for defence applications in last three decades.

 

Keywords: Piezoelectric transducer, hydrophone, actuator, detonator , SONAR, MEMs, Gyroscope

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O-6A                                                                                               59

Thermal stress induced Acoustic Emission (AE) signals from soft PZT ceramics

 

K. Prabakar¹, S. Manjunath Rao² and S.P. Mallikarjun Rao¹

 

¹Physics Department, Univ. college of Sc., Osmania Univ., Hyderabad – 500 007

²Central Instrumentation Lab., University of Hyderabad, Hyderabad, India

 

Sound emissions from commercially important soft PZT ceramics namely PZT5A, PZT 5J, PZT 5H of both poled and unpoled nature were studied in the temperature range of ambient to about 300ºC. In the case of unpoled PZT ceramics, a cluster of Low Frequency Acoustic Emission (LF-AE) signals around 60ºC were observed and are attributed to the debonding / escape of gaseous matter trapped during the firing of  counter electrodes. The LF-AE signals observed from 100ºC to till about the Phase Transition temperature were attributed to the micro cracks generated within the sample due to thermal inhomoginities and the lattice parameter changes. Where as in the case of poled samples, apart from these LF-AE signals, High Frequency Acoustic Emission (HF-AE) signals were also observed and are attributed to the domain fallbacks due to the depoling of the sample. In the case of PZT 5A and PZT 5J, the depoling signals were observed till the sample reaches its Curie Temperature (Tc), indicating that these samples are not completely depoled even when they reach their Tc. Where as the absence of HF-AE signals in the case of PZT 5H showed that these samples were completely depoled by the time they reach the Tc. It was observed that these HF-AE signals normally cluster around 100ºC and 200ºC. Even in the unpoled sample some of the HF-AE signals are observed and are attributed to the random fallbacks of the domains. The results are supported by micro photographs.

Keywords:  PZT ceramics, Acoustic Emission, thermal stress.

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PA-09                                                                                                                       32

PYROELECTRIC CHARACTERIZATION OF

MAGNETOELECTRIC NBT-BiFeO₃ SOLID SOLUTIONS

 

E.Venkata ramana, S.V.Suryanarayana and T.Bhima Sankaram

 

Materials Research Lab., Dept. of Physics, Osmania Univ., Hyderabad-500007.

ramana_evr@rediffmail.com

 

Sodium bismuth titanate, Na_1/2Bi_1/2TiO₃ (NBT) is considered to be an important lead-free material. It has relatively high polarization limits (38mC/cm² ,Ec=70kV/cm) and a curie temperature(T_C) of 320^oC. The sequence of phase transitions is: Rhombohedral (RT)-Tetragonal (200-300^oC)-Cubic (520-540^oC). NBT based solid solutions with BaTiO₃, PbTiO3, SrTiO3 have resulted in good piezoelectric properties. Bismuth ferrite, BiFeO₃ (BF), belongs to a class of materials showing simultaneous ferroelectricity and magnetism. It is an antiferromagnetic with Neel temperature (T_N=370^oC). It has high ferroelectric transition temperature (850^oC). The solid solution system 1-x NBT-x BF(x=0-0.4) is prepared through the solid-sate double sintering method. Phase confirmation and lattice parameter were evaluated by XRD.  Pyroelectric measurements were performed by a static method. Pyroelectric coefficient of 7X10^-8 C cm^{-2 o}C^-1 was observed for x=0 composition which increases with the increase of BF content in NBT. Pyroelectric figure of merits for all the compositions were calculated from the value of p. From the data on temperature variation of dielectric constant, the T_C were also evaluated. The results are discussed.

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PA-10                                                                                                                     113

DIELECTRIC PROPERTIES OF STRONTIUM BARIUM NIOBATE SYNTHESIZED BY PECHINI METHOD

 

Mohan P. Pathak, P. K. Patro and A. R. Kulkarni

Dept.of Metallurgical Engg. & Materials Science, I.I.T Bombay, Mumbai-400 076

ajit.kulkarni@iitb.ac.in

 

Strontium Barium Niobate (SBN), a relaxor ferroelectric with tetragonal tungsten bronze structure, has wide applications in electro-optic/electromechanical devices. In the current work, synthesis of Sr_xBa_1-xNb₂O₆ with x = 0.5 by Pechini method has been achieved successfully for the first time. The precursor obtained by Pechini method was calcined at 650^°C and the resulting powder was recalcined in the temperature range of 650-900^°C. Powder pellets were then sintered at 1250^°C, resulting in formation of single phase SBN with uniform microstructure. Dielectric properties were measured in the frequency range of 100 Hz to 1 MHz from room temperature to 200°C. Typical relaxor behaviour was observed with a maximum dielectric constant of 1881 (Tc~50 ^oC) at 1 KHz. P-E hysteresis loop studies were carried out. The values of P_s and E_c are comparable with the reported values.

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PA-11                                                                                                                    106

STRUCTURAL AND ELECTRICAL STUDY OF

NEW RELAXOR MATERIAL Pb(Ba_1/3Nb_2/3)O₃

 

Mukul Pastor, P.K.Bajpai* and R.N.P. Choudhury**

*School of Pure & Applied Physics, Guru Ghasidas Univ., Bilaspur – 495009

**Department of Physics and Meteorology, I.I.T Kharagpur 721302, India

 

The ferroelectric ceramics Pb(Ba_1/3Nb_2/3)O₃ (PBN) synthesized by a solid state reaction technique and structurally characterized using XRD and SEM.  The X-ray diffraction of the sample at room temperature shows a rombohedral perovskite structure with a small percentage of cubic pyrochlore phase. The field dependence of dielectric response and the conductivity are measured in a frequency range 10 KHz, 10 KHz and 100 KHz and in temperature range from -25°C to 182°C. The frequency dependence of dielectric loss peak is found to obey an Arhenius law. An analysis of the real and imaginary part of the dielectric permittivity with frequency is performed, assuming a distribution of relaxation times as conformed by Cole-Cole plots as well as the scaling behavior of the dielectric loss. The scaling behavior of dielectric loss spectra suggests that the distribution of the relaxation time is temperature dependence.    

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PA-12                                                                                                                       63

RELAXOR BEHAVIOUR IN

Pb[(Mg_3/4Co_1/4)_1/3Nb_2/3]O₃ CERAMIC

 

                   Amit Kumar, K. Prasad, S.N. Choudhary^# and R.N.P. Choudhary^*

 

^#Material Research Lab., Univ. Dept.of Physics,T.M.Bhagalpur Univ. Bhagalpur

      ^*Department of Physics and Meteorology, I.I.T, Kharagpur - 721 302, India. 

snchy_83@rediffmail.com

 

Lead based perovskites with the general formula Pb[B¢_1/3B²_2/3]O₃ (B¢ = Mg⁺², Zn⁺², Ni⁺², Co⁺² etc and B² = Nb⁺⁵, Ta⁺⁵ etc.) have been widely studied for their possible application in multilayer capacitors (MLCs). These materials are found to possess a value of dielectric constant ~ 10³ and a higher degree of diffuseness in the phase transition. In the present work we report the study of structural and dielectric properties of Pb[(Mg_3/4Co_1/4)_1/3Nb_2/3]O₃  ceramic.

 

Polycrystalline samples of Pb[(Mg_3/4Co_1/4)_1/3Nb_2/3]O₃ were prepared by using two stage high temperature columbite precursor method. From the XRD study, it has been found that the compound possesses single-phase cubic structure. Detailed studies of the dielectric constant (e) and loss tangent (tanδ) with temperature at different frequencies were carried with a computer controlled LCR-Hitester (3532-50) suggest that the compound undergoes diffuse phase transition. The observed value of the transition temperature (T_C) at frequency 1kHz, 10kHz, 100kHz and 1MHz were found to be –12^oC, -10^oC, -8^oC and –4^oC respecctively. Fitting of dielectric data to the Vogel-Fulcher relation indicated that Pb[(Mg_3/4Co_1/4)_1/3Nb_2/3]O₃ behaves like a spin-glass system. Impedance analysis shows that bulk conductivity of the material increases with rise in temperature.

Acknowledgement:The authors acknowledge financial support of DST, N.Delhi.

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PA-13                                                                                                                       74                                                                                                               PEROVSKITE PHASE OF PMN-PT FEBRICATED

AT LOW TEMPERATURE

 

Neetu Bargoti and S. K. Singh^*

 

School of Pure and Applied Physics, Guru Ghasidas University, Bilaspur-495009

 

Lead magnesium niobate Pb(Mg_1/3Nb_1/3)O₃ (PMN) is one of the most interesting relaxor ferroelectric materials from a fundamental viewpoint. PMN forms a crystalline solid solution with a normal ferroelectric PbTiO₃ (PT) and its solid solution of 10 mol% PT leads to a maximum dielectric constant temperature (T_max) close to room temperature, whilst maintaining high dielectric properties and relaxor behavior. PMN stabilizes through a morphotropic phase boundary at about 35 mol% of PT. Addition of PT over 35 mol% in PMN shows normal ferroelectric behavior. This is thought to be due to the disturbance of the local Mg:Nb ordering by the addition of Ti ions. It is difficult to fabricate pure and stoichiometric PMN-PT solid solution, due to compositional complexity and poor thermodynamic stability of the perovskite phase compared to the pyrochlore phase and  Pb loss during fabrication.

The samples were prepared by columbite precursor method. In the first stage, MgNb₂O₆ was fabricated by mixing MgO and Nb₂O₅. In the second stage the PMN-PT perovskite solid solution were fabricated by reacting the above precursors with PbO and PbTiO₃ at 830ºC using liquid grinding. The samples were sintered at 800ºC for 4h in a covered platinum crucible. The XRD patterns of sintered PMN_1-x-PT_x (x = 0.0 – 0.30) samples observed single (200) peak shows the ferroelectric rhombohedral phase, while x = 0.35 and above shows the splitting of (002) and (200) peaks indicates that they are the ferroelectric tetragonal phase. When x = 0.30 – 0.35, we have observed the mixed phases of ferroelectric rhombohedral and tetragonal. After refinement, we can see the monoclinic phase, when x = 0.33 as observed by the B. Nadia et al and D. Panday el al. We have successfully fabricated perovskite phase of solid solution of PMN-PT at low temperature without using excess lead. 

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PA-14                                                                                                                       42

EFFECT OF SINTERING TEMPERATURE ON THE MICROSTRUCTURE AND DIELECTRIC PROPERTIES OF PbO AND MgO DOPED 0.8 PMN – 0.2 PT

 

Yogesh Sharma, Anjan Sil and K.L. Yadav*

 

Department of Metallurgical and Materials Engineering

 *Department of Physics, I.I.T. Roorkee, Roorkee–247 667

klalyfph@iitr.ernet.in

 

Solid Solution in the system (1-x) Pb (Mg_1/3 Nb_2/3) O₃ – (x) PbTiO₃ [PMN-PT] (where x = 0.0-0.35) is a well-known relaxor ferroelectrics material having very high dielectric constant. This material has received considerable attention for its applications in thin film capacitors, mechanical actuators and transducers. PMN-PT ceramics undergo ferroelectric phase transition over a wide temperature range and this transition  is known as diffuse phase transition (DPT).

Pyrochlore phase formation, even in small quantity, during the processing of perovskite solid solution in the lead based relaxor system PMN-PT is detrimental for dielectric behavior. There are several processing routes available by which the formation of undesirable pyrochlore phase could be suppressed, among these the columbite processing technique in which prefabricated MgNb₂O₆ is made to react with an appropriate proportion of PbO, has been widely used in the synthesis of phase pure perovskite PMN - based materials.

In the present work, PMN was prepared by two different routes i.e. single step mixing and columbite precursor (multi step), in order to reduce the pyrochlore phase formation using different calcination condition. The pyrochlore phase was reduced from 25% to 10% by using various calcination conditions and found that calcinations at 900⁰C for 4hr in PbO rich atmosphere is the best calcination condition. In the present paper we report our work on 0.8PMN – 0.2PT solid solution prepared by columbite precursor method. The specimens were sintered at two temperature 900⁰C and 1000⁰C for 4hr.   The samples were characterized by X-ray diffraction for phase purity and Scanning Electron Microscope for micro-structural development. Dielectric measurements as a function of temperature were carried out by the LC meter. Particle size and density was observed to vary with sintering temperature, which has been correlated to the dielectric constant. Microstructure modification was observed by adding excess PbO and MgO (1 wt.% each) to the solid solution  and these results were also correlated to the dielectric constant, which shows that excess PbO reduces the dielectric constant while excess MgO raises the dielectric constant.

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PA-15                                                                                                                   55

INVESTIGATIONS ON RELAXOR MODIFIED

Pb_0.76Ca_0.24TiO₃ CERAMICS.

 

A.P.Kulkarni, D.J.Salunkhe, S.R.Kokare, S.B.Kulkarni and P.B.Joshi

 

Department of Physics, Solapur University, Solapur – 413 255.

drpbjoshi@rediffmail.com

 

The Pb_0.76Ca_0.24­TiO₃ is known to be a useful piezoelectric transducer for low power NDT and high frequency medical imaging systems. The material is known to possess substantial dielectric anisotropy d₃₃/d₃₁ but a low value of Q_M. It was our interest to investigate the PbCaTiO₃ system with compensating off valency substitution to understand, whether any Relaxor type of behavior and improvement in the d₃₃ and d₃₃/d₃₁ occurs.

The compositions investigated are Pb_0.76Ca_0.24Ti⁴⁺_(1-x)Nb⁵⁺_x/2 (Cr²⁺_x/4Ti⁴⁺_x/4)O₃, with x varying between 0 to 0.05. The Ti is substituted in a compensating off valency form where the Ti_x is substituted by Nb⁵⁺_x/2 (Cr²⁺_x/4Ti⁴⁺_x/4). The sintering schedule was designed properly, using simultaneous investigations of the XRD, to stabilize the Cr ions in state 2+. The material is studied for the structural properties (XRD), IR absorption studies, electric permittivity as a function of temperature and frequency both, complex impedance spectra (both below as well as above Tc), piezoelectric parameters e.g. d₃₃, d₃₁, K_p, N_p, Y^o_E etc. and pyroelectric properties. The composition with x=0.02 has shown improved piezoelectric parameters for device applications.

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PA-16                                                                                               13

DIELECTRIC RELAXOR CERAMICS – SOLID SOLUTION

OF Na_0.5Bi_0.5TiO₃ WITH Ba(Nd_0.1Ti_0.8Nb_0.1)O₃

 

Syed Mahboob ^a, A.R.James ^c, Chandra Prakash ^b, G.Prasad ^a and G.S.Kumar ^a

 

^a Materials Research Lab., Dept. of Physics, Osmania Univ., Hyderabad-500 007

^b Solid State Physics Laboratory, Delhi-54, India.

^c Defence Metallurgical Research Laboratory, Kanchanbagh-500 058, Hyderabad

gskumar1948@sify.com

 

Ceramic compositions [Ba(Nd_0.1Ti_0.8Nb_0.1)O₃]_(1-x)[Na_0.5Bi_0.5TiO₃]_x         (BNNT_(1-x)-NBT_x) with x = 0.0,0.25,0.40.0.50,0.55 were prepared  by modifying the relaxor dielectric material Ba(Nd_0.1Ti_0.8Nb_0.1)O₃  with  ferroelectric Na_0.5Bi_0.5TiO₃ using conventional solid state sintering route. The X-ray diffraction studies revealed that the ceramic compositions x= 0.0, 0.25, 0.40, 0.50, 0.55 are of simple cubic structure at room temperature. Dielectric measurements carried over a wide range of temperature (80K to 300K) and at different constant frequencies (10kHz, 50kHz, 100kHz, 500kHz and 1MHz) revealed that all the ceramic compositions exhibited dielectric dispersion with frequency and the temperature of dielectric maximum shifted towards higher temperature side with increase of frequency characterizing the typical relaxor behaviour.  The substitution of NBT in BNNT has increased the temperature of dielectric maximum. This increase in dielectric maximum temperature can be correlated to the steric effect arising due to the replacement of A-site ion (Ba⁺² ≈ 149 pm) with smaller ions (Na⁺ ≈ 116 pm, Bi⁺³ ≈ 117 pm). The data on dielectric and room temperature resistivity would be presented.

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PA-17                                                                                                                       36

DIELECTRIC STUDIES OF 0.85 PMZN-0.15 PT SOLID SOLUTION

 

                   Amit Kumar, K. Prasad, S.N. Choudhary^# and R.N.P. Choudhary^*

^# Materials Research Lab., Univ. Dept. of Physics,T.M.Bhagalpur univ.,Bhagalpur

^*Department of Physics and Meteorology, I.I.T. Kharagpur - 721 302

snchy_83@rediffmail.com

 

Complex  lead based perovskites having general formula Pb(B′_1/3 B″_2/3)O₃ exhibiting diffuse phase transition are a promising candidate for ceramic electrostrictive actuators as well as for multilayer ceramic capacitors. Lead magnesium zinc niobate Pb[(Mg_3/4Zn_1/4)_1/3Nb_2/3]O₃ (PMZN) is one of the relaxor ferroelectrics having phase transition temperature near 40^oC at 1kHz, but it increases with the addition of PbTiO₃ (PT), which is a normal ferroelectric perovskite.

Solid solution of 0.85Pb[(Mg_3/4Zn_1/4)_1/3Nb_2/3]O₃ 0.15PbTiO₃ was prepared by using the two stage high temperature Columbite processing technique. XRD analysis shows the formation of a single phase tetragonal structure. The dielectric studies carried over a wide temperature (32^oC-250^oC) and frequency range (1kHz-1MHz) exhibits the diffuse phase transition with relaxor behavior. These materials have some features analogous to magnetic spin glass and the Vogel-Fulcher equ. often used for describing observed temperature dependence of cluster dynamics.

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PA-18                                                                                                                       47

STRUCTURAL AND ELECTRICAL PROPERTIES

OF PMNN CERAMIC

 

                   Amit Kumar, K. Prasad, S.N. Choudhary^# and R.N.P. Choudhary^*

 

^#Materials Research Lab., Univ. Dept. of Physics,T.M.Bhagalpur univ.,Bhagalpur

      ^*Department of Physics and Meteorology, I.I.T., Kharagpur - 721 302

snchy_83@rediffmail.com

 

The study of ferroelectric materials and their various applications has recently drawn the attention of scientists for both research and technological development. Among these ferroelectric materials, some oxides with the perovskite structure having a general formula ABO₃ (A= mono/divalent, B= tri/ tetravalent ions) are in the forefront area of research for their use in device applications. In view of this an attempt has been made to study some modified PMN ceramics having a general formula Pb[(B¢_3/4B²_1/4)_1/3Nb_2/3]O₃ (B¢=Mg⁺², and B²= Zn⁺²,Ni⁺² etc). Polycrystalline sample of   Pb[(Mg_3/4Ni_1/4)_1/3Nb_2/3]O₃ (PMNN) were prepared by the high temperature columbite precursor method. The preliminary X-ray diffraction studies suggest the formation of the single phase compound with a cubic structure(a=4.042(8)A°). The temperature dependence of e and tanδ at different frequencies (1kHz-1MHz) shows diffuse phase transition and the relaxor behaviour having T_C below room temperature for various frequencies. The d.c. conductivity was calculated from the complex impedance plot of the sample in the temperature range 32^OC to 250^OC. The variation of d.c. conductivity with temperature exhibit the semiconductor characteristic of the samples. The a.c. conductivities were also calculated from the dielectric data at different temperatures and frequencies.  

 

PA-19                                                                                                                       51

GROWTH OF RELAXOR FERROELECTRIC 0.91Pb(Zn_1/3Nb_2/5)O₃-0.09PbTiO₃ SINGLE CRYSTALS  BY FLUX-BRIDGMAN MEHTOD AND THEIR CHARACTERIZATIONS

 

G. Madeswaran, J. Bubesh Babu, S. Moorthy Babu and R. Dhanasekaran*

 

Crystal Growth Centre,

Anna University, Chennai – 600 025.

rdhanasekaran@annauniv.edu

 

Relaxor ferroelectric single crystals of (1-x)Pb(Zn_1/3Nb_2/3)-xPbTiO₃ with perovskite structure exhibit a high dielectric constant, large piezoelectric coefficient, an extremely high electromechanical coupling factor and a very large strain at the morphotropic phase boundary (MPB) of the system and it appears near the composition of 9% PT content.  Such outstanding performance makes these crystals one of the most promising candidates for electromechanical transduction in a broad range of advanced applications such as medical ultrasound imaging and underwater communications.

 

0.91Pb(Zn_1/3Nb_2/3)O₃-0.09PbTiO₃ [0.91PZN-0.09PT] single crystals have been grown by flux-Bridgman method.  The stoichiometric proportions of ZnO, Nb₂O₅ have been calcined at 1000⁰C for 10h.  The presynthesised powder has been mixed with stoichiometric proportion of TiO₂ and Pb₃O₄ and calcined at 750⁰C for 2 h. 0.91PZN-0.09PT single crystals have been grown by flux-Bridgman method using Pb₃O₄ flux. The mixture of the synthesised 0.91PZN-0.09PT and flux (Pb₃O₄) has been taken in the ratio of 45:55 mol%.  After soaking for about 10 h at 1200⁰C, the crucible has been lowered at the rate of 1 mm/h upto 900⁰C and then cooled to room temperature at the rate of 60⁰C/hr.  An addition of small amount of B₂O₃ with Pb₃O₄ flux used to increase the dissolving power of the melt, and to create an optimum degree of complex formation and an optimum viscosity.  Due to its low melting point and high viscosity, B₂O₃ could also form an encapsulate layer preventing the flux evaporating and the crucible from being attacked by the molten Pb₃O₄ at high temperatures.  All these effects contributed to the improvement of the flux effectiveness, leading to a more stable growth.  The growth results, dielectric and morphological studies will be discussed in detail. 

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PA-20                                                                                                                       52

GROWTH AND CHARACTERISATION OF RELAXOR FERROELECTRIC Pb[(Zn_1/3Nb_2/3)_0..91 Ti_0.09]O₃

SINGLE CRYSTAL

 

J. Bubesh Babu, G. Madeswaran, S. Moorthy Babu and R. Dhanasekaran

 

Crystal Growth Centre, Anna University, Chennai – 600 025

rdhanasekaran@hotmail.com

 

Pb[(Zn_1/3Nb_2/3)_0..91Ti_0.09]O₃ solid soution (PZN-PT) is a novel material used for piezoelectric transducer applications. These lead-based relaxor single crystals are very promising for a compositions near morphotropic phase boundary (MPB) and shows exceptional properties such as electromechanical coupling coefficient k₃₃ > 90 %, piezoelectric coefficient d₃₃ > 2000 pC/N and very high dielectric constant. These single crystals have a very wide range of applications such as medical ultrasound imaging, and underwater SONAR transducer applications. These crystals can replace the PZT ceramics very effectively. The pyrochlore phase is the parasitic phase tries to dominate the perovskite phase. Single crystals of PZN-PT were grown by Flux technique and bottom-supported flux Bridgman method with 55 mol % of PbO flux. There are too many issues to overcome, (i) inducing a single nucleus and growth of that particular nucleus is too difficult (ii) maintaining a single melt-solid interface throughout the growth period is also difficult. These lead to multinucleate and the obtained crystal size is poor. The growth of PZN-PT by modified flux Bridgman method can effectively control the multinucleation problem. Still then the growth parameters like gradient of the furnace, translation rate and flux-precursor ratio etc., play a key role in optimizing the size and properties of the grown crystals. The X-ray powder diffraction studies of grown PZN-PT single crystal have been carried out. The results show that the grown crystals are in pure perovskite phase. The thermal stability of the grown crystals is characterized by DTA and TGA studies. The dielectric studies have been made to confirm the phase transitions and the curie temperature of the grown crystal.

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PA-21                                                                                                                       39

STRUCTURAL AND DIELECTRIC STUDIES OF

0.80Pb[(Mg,Zn)_1/3Ta_2/3]O₃ – 0.20 PbTiO₃ CERAMIC

 

S.Prasad*, K. Prasad, S.N. Choudhary and T.P. Sinha^#

 

Material Resaerch Lab., Univ. Dept.of Physics,

T.M.Bhagalpur Univ.,Bhagalpur

^#Department of Physics, Bose Institute,

93/1 A.P.C. Road, Kolkata-700009.

sprasadbgp@sancharnet.in

 

Since the discovery of relaxor properties in Pb(Mg_1/3Nb_2/3)O₃ (PMN), a large number of oxide perovskites having a general formula Pb(B¢_1-xB²_x)O₃ have been studied. Recent studies show that lead magnesium tantalate Pb(Mg_1/3Ta_2/3)O₃ (PMT) is an important material for various electronic applications. Since the ferro-paraelectric transition temperature of PMT is around -90^oC it can not be used for many electronic devices as such. PbTiO₃ is a normal ferroelectric having high value of transition temperature (T_C) around 490^oC. Addition of lead titanate shifts the T_C of PMT significantly, which can be useful for several applications.

The solid-solution of 0.80 Pb[(Mg_2/3Zn_1/3)_1/3Ta_2/3]O₃ – 0.20 PbTiO₃ was prepared by columbite precursor method. The formation of the compound was checked by X-ray diffraction technique. The compound was found to possess tetragonal structure at room temperature. The dielectric constant (e) and loss tangent (tand) as a function of temperature over the frequency range 10kHz to 1MHz was measured using a computer controlled LCR-Hitester (3532-50 HIOKI, Japan). It is observed that the compound exhibits a diffuse phase transition. It is observed that the addition of 10% PbTiO₃ shifts transition temperature just above to room temperature. Fitting of dielectric data to the Vogel-Fulcher relation indicated that the compounds behaves like a spin-glass system. The admittance spectroscopy using the variation of real part of admittance (Y) versus imaginary part of Y at room temperature shows glassy nature of the compounds. The frequency variation of impedance at different temperatures, show the bulk conductivity of the material increasing with a rise in temperature.

 

 

Acknowledgement: The authors (K P and SNC) wish to acknowledge the financial support from DST, New Delhi under contract no. SP/S2/M-15/97.

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SESSION III B

CRITICAL ISSUES IN FERROELECTRICS

Wednesday, November 24, 2004

09.00 A.M.   -    11.00 A.M.

                                                                            

I-06B                                                                                            120

Recent Investigations on Ferroelectric

Glycine Phosphite Single Crystals

 

S. Vanishri, A Deepthy and H.L.Bhat

Department of Physics, Indian Institute of Science, Bangalore-560012.

 

Glycine Phosphite ( NH₃CH₂COOH₃PO₃ ), abbreviated as GPI, is a recently discovered  ferroelectric crystal which exhibits a second-order paraelectric-ferroelectric transition at 224.7 K. The spontaneous polarization appears perpendicular to the phosphite chains i.e., parallel to b-axis. GPI belongs to space group P2₁/a at room temperature and P2₁ below T_C. The ferroelectric phase transition in GPI is related to the ordering of the protons in the interphosphite hydrogen bonds and to the dynamics of the glycinium cations. The present work discusses some of our recent work on this crystal viz. the crystal growth, dielectric properties, effect of X-ray irradiation on phase transition, polarization switching process and determination of elastic constants.  

Single crystals of GPI were grown by slow cooling technique and by controlled evaporation. In the growth runs involving slow cooling, a cooling rate of 0.02 °C/ h from 309 to 303 K was adopted. Thermal analysis carried out on the crystals showed that the crystals are stable up to 149 °C. Differential scanning calorimeter curve exhibited an anomaly in the heat flow at about 224.5K, indicating a phase transition. Morphology of the crystal has been determined using contact and optical goniometer. The grown crystals were characterized for their defect content by chemical etching on (010) plate, the EPD thus calculated is 600/cm². Dielectric measurements carried out on b-cut plates in the temperature range 200-300K for various frequencies showed substantial dispersion close to T_C. Thickness dependence of the dielectric properties revealed the presence of a non-ferroelectric surface layer of a low dielectric constant in the crystal.  The effect of X- ray irradiation on the structural and dielectric properties  across the  ferroelectric phase transition were studied. The peak value of dielectric constant reduced progressively with the exposure time and a shift in phase transition temperature towards the lower temperature was observed. These changes in the dielectric properties were identified to be due to the formation of PO₃^2- radicals by electron paramagnetic resonance.  The domain dynamics in GPI was investigated by polarization switching studies carried out using the Merz technique. The experimentally observed switching curves were fitted to a model based on Pulvari-Kuebler theory of  nucleation and growth of domains. It is observed that the switching process in this crystal is governed by a linear forward growth process in the high field region. Elastic properties of GPI were investigated using ultrasonic technique at room temperature and across phase transition.   Pulse Echo Overlap method is used for measuring the velocity of ultrasonic waves in the sample. All the thirteen elastic stiffness and compliance constants of GPI were determined. Correlation of this data with the crystal structure explains the high value of elastic constant along the crystallographic b direction and smaller values along the a and c directions. The variation in ultrasonic velocity across the phase transition temperature reveals an order-disorder type paraelectric-ferroelectric phase transition at around 224 K.

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I-07B                                                                                              49

RELIABILITY ISSUES OF FERROELECTRIC

RANDOM ACCESS MEMORIES

 

S. K. Singh^1,2 and H. Ishiwara¹

¹Interdisciplinary Graduate School of Science and Engineering,

Tokyo Institute of Tech., 4259 Nagatsuda, Midori-ku, Yokohama 226-8503, Japan

²School of Pure and Applied Physics, Guru Ghasidas University, Bilaspur-495009

singh@neuro.pi.titech.ac.jp

 

The reliability of ferroelectric capacitors as well as CMOS circuits is one of the most crucial issues in the commercialization of FeRAMs, as both ferroelectric capacitors CMOS circuits need to be highly reliable for at least 10 years and to allow a number of read/write cycles larger than 10¹⁵.  In case of the ferroelectric memory cell, failure mechanisms such as polarization fatigue, retention loss, and imprint have been reported in the literature, which can affect the operation. The physical origin of these failure mechanisms is still under discussion but main concentration is on defects at the interface between the electrode and the ferroelectric films. The ferroelectric-gate FETs with MFMIS gate structures using Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films capacitors were fabricated. Considering that the defects are oxygen vacancies, we substitute the Ce at Ti-site in the BLT films, to utilize the Ce properties. CeO₂ has been used in catalytic reactions and it is believed that the reducibility of CeO₂ contributes to oxygen storage and release capability, which enhance oxidation and charge trapping. Memory cell structure was fabricated and carries out server electrical characterization. The leakage current density of the Ce⁴⁺ doped BLT films is found to be lower than those in pure BLT films. 0.03% doped films showed fatigue-free response up to 10¹⁰ switching cycles. We were observed that polarization increases with the switching cycles as we doped Ce in BLT capacitors more than 0.03%. When the switching voltage amplitude rises, the polarization started increasing earlier in fatigue measurement. Polarization increases in measurement of fatigue can be express using wakeup phenomenon or charge injection, when continuous pulse trains are applied. Control of oxygen vacancies and reliability of FeRAMs devices are crucially issue, which we will discuss during the 13^th NSFD.     

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I-08B                                                                                            119

INTEGRATED FERROELECTRIC TECHNOLOGY

AND RECENT TRENDS

 

H.V. Tiwary

Pt. Ravishankar Shukla University, Raipur (C.G.)

 

The recent trend of research and development in the preceding one and half decade has lead to novel field of integrated ferroelectrics technology. The initial step for this research and development were on preparation of thin film ferroelectrics. The next steps of studies were on the semiconductor/ferroelectrics interface, field effect transistors and devices with special emphasis on sub micron level memory devices. There has been substantial research and development in application of ferroelectrics and related properties for transducers and sensor devices. Our research group has contributed in the above two fields.

On the other hand the electro-optic and optical nonlinear behavior and second harmonic generation properties of ferroelectrics thin film material were subjected to optoelectronics device application studies. We have studied some soft ferroelectrics thin films for optical wave-guide applications. In addition to optical wave-guide studies the recent trends and patents were also in the exploration of the field of optical memory and optical disk use in modern computer. So the future of ferroelectrics thin film technology together with semiconductor ferroelectrics integration in MOSFET’S and Optoelectronics application of ferroelectrics has paved its way to new field of integrated ferroelectrics technology.

The presentation of this invited talk is to review the above recent trends in research and development in the field of integrated ferroelectrics together with some of our research group contribution in this new field.

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O-04B                                                                                          146

STUDIES ON DIELECTRIC PROPERTIES OF PROPERTIES OF PEROVSKITE BASED Sr_1-xGd_xTi_1-xCo_xO₃(x<0.50) SYSTEM

 

H.S.Tewari

School of Pure & Applied Physics, Guru Ghasidas Univ., Bilaspur–495 009 (C.G.)

 

The electronic ceramics are gaining importance for their specific dielectric, electrical and magnetic applications. These electronic ceramics are widely used in the areas of energy, electronics, electricity, automobiles and related products. In these materials, bulk structure, nature, of grain of grain boundaries and surfaces play an important role in deciding the resulting properties. The largest group of ferroelectrics and related materials is based on the simple perovskite structure ABO₃. One of the major advantages with this class of materials is the possibilities to tailor make their properties by compositional modification (appropriate substitution on A site or B site independently or A and B both the sites simultaneously) or by suitaby controlling the processing parameters used for their preparation. For example, it was shown that the dielectric characteristics of this class of materials can be considerably changed by changing the route of syntheses, time and temperature of calcinations and sintering, cooling rates from sintering temperature to room temperature etc.  In recent investigations on valence compensated perovskite oxide of the type Sr_1-xLa_xTi_1-xCo_xO₃ reveal the formation of barrier layers at much lower temperature by sintering in air. In view of the interesting and useful properties of this system, it is considered worthwhile to synthesize and explore the dielectric properties of analogous new series of the type Sr_1-xGd_xTi_1-xCo_xO₃ which represents the solid solution between insulating oxide strontium titanate and semi conducting oxide gadolium cobaltite. The compositions with x= 0.10, 0.30 and 0.50 in the above system were prepared by solid-state ceramic method. The dielectric properties of these materials are explained by considering the presence of microscopic chemical heterogeneities arising our of the slow diffusion controlled solid state sintering process used for their preparation. the dielectric characteristics have also been analyzed using complex plane impedance analysis.

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O-05B                                                                                            48

SHAPE MEMORY EFFECT IN PMN-PT(70/30)

 FERROELECTRIC CERAMIC

 

Pragya Pandit, Surya M. Gupta and V. K. Wadhawan

Ceramics Laboratory, Laser Materials Division, CAT, Indore 452013

   

Lead based ferroelectric ceramics are well known for their use in sensors and actuators. Here we report the observation of shape-memory effect (SME) in a solid solution of lead magnesium niobate-lead titanate (PMN-PT) in the 70/30 ratios. Recovery of a pseudo-plastically deformed material to its original shape on heating is called the SME. Shape memory alloys are being explored by the aerospace industry for use in movement of flaps, which will replace the existing extensive hydraulic systems. The shape memory effect is currently being exploited in the space shuttle also. The SME reported here was observed by bending and thermal-cycling experiments. A fully recoverable shape strain of ~0.2% has been found by us for this composition, which is in the same range as that reported for PMN-PT(65/35). A simple symmetry analysis indicated the existence of “crystallographic reversibility” for our thermal cycling experiments. The SME in the  ferroelectric composition investigated by us is due to the presence of the ferroelastic phase transition and the reversible alignment of ferroelectric domains under the mechanical bending field. Effect of electric field, bending load, and thermal cycling on the shape strain and ferroelastic phase transition will be presented, as also the results of phase, polarization and dielectric analyses.

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O-06B                                                                                          111

STRUCTURAL AND DIELECTRICAL MODIFICATION BY Bi DOPANTS ON PLZT CERAMICS

 

Seema Sharma*, Radheshyam Rai^@ and Prof. R. N. P. Choudhary**

*Dept.of Physics, BITS PILANI GOA Campus, Zuari Nagar-403726, Goa

^@Electronic Materials Division, National Physical Lab., N.Delhi 110012

**Department of Physics, I.I.T., Kharagpur –721310,

 

The ferroelectric phase transition represents special class of structural phase transition characterized by the appearance of a reversible spontaneous polarization below a Curie temperature. Below this temperature and in the absence of applied d.c. electric bias, there are at a minimum two crystallographically equivalent directions along which spontaneous polarization can develop. To minimize the depolarization fields in a highly insulating materials, different regions of the crystal polarize along different crystallographic direction [1]. The volumes of uniform polarization are called domains. The resulting domain structure usually appears in such a way that the polarization is near-completely compensated. However, this mechanism is not necessarily universal because multi domain structure are also known to exist in highly conductive crystals of PbTiO₃, where the depolarizing filed could easily be compensated for by the migration of free carriers. The formation of a multi-domain structure in either case can be described by the transformational elastic strain energy argument[2].          There exists a particular class of ferroelectric known as relaxors which exhibits diffuse phase transition. These materials are characterized by shift of the dielectric permittivity maximum with frequency and the absence of any macro-symmetry changes at a structural transformation. Relaxor behavior is believed to arise due to a compositional and structural heterogeneity which act to break the translational invariance of the polarization. In this paper, we report the study of the tetragonal PLZT and monoclinic PLBZT i.e. Pb_0.9(La_xBi_1-x).1(Zr_0.65Ti_0.35)_0.975O₃ (x=0.0, 0.3, 0.5 and 0.7) system. Polycrystalline samples of double-doped PZT were synthesized by high- temperature solid- state reaction technique. Preliminary crystal structure and micro- structure of the compounds were studied using X-ray diffraction techniques. Detailed dielectric studies of the samples suggest that they undergo second order ferroelectric-paraelectric diffuse phase transition. The change in the values of the dielectric constant and dissipation factor with Al concentration show very interesting behavior of the compound. Temperature dependence of d.c resistivity has also provided some interesting features.

References:

[1] Lines. M. and Glass A. 1977 Principles and Application Ferroelectric and Related Materials.

[2] Khachaturayan A. 1983, Theory of structural Transformation in solids (New York: Wiley)

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PA-22                                                                                                         121

Electrical properties of samarium modified lead titanate ceramics with

liquid phase additives

 

Sarabjit Singh, O.P. Thakur and Chandra Prakash

 

Electroceramics Group, Solid State Physics Lab., Lucknow Road, Delhi-110054

prakash@ssplnet.org

 

Lead titanate is a perovskite-type ferroelectric with a Curie temperature of about 490^oC.  This in pure form has high value of tetragonality (1.063), which results in microcracking during cooling through the transition temperature. To make usable lead titanate, it is necessary to reduce the tetragonality. It is achieved by proper substitutions. Another way to circumvent the problem of fragile nature is by liquid phase sintering using suitable flux agents.  In the present work, an attempt has been made to stabilize the lead titanate with very small amount of samarium substitution at A site and also by the addition of flux (Bi₂O₃ and Li₂O).

Pb_0.98Sm_0.02TiO₃ composition with different amounts of Bi₂O₃ + Li₂O (4 and 8 wt %) were prepared by conventional ceramic route. Powders were calcined twice at 800^oC and 850^oC respectively for 4 hrs followed by ball milling. Pressed discs were then sintered at 1150^oC and 1250^oC for 4 hrs in lead rich atmosphere.  The phase formation was confirmed by X-ray diffraction patterns.

Dielectric properties were studied as a function of frequency (10 kHz-1 MHz) and temperature (RT to 550^oC). All the samples show well-defined ferroelectric behaviour. Curie temperature (T_c) determined from dielectric constant vs. temperature plots, was found to decrease with increasing sintering temperature and also with the increase in liquid phase. The detailed results shall be reported.

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PA-23                                                                                                                       53

MICROWAVE SINTERING OF IRON DOPED

PZT AT 2.45GHz

 

Mayank Tiwari, Virendra Singh, H. H. Kumar, D. K. Kharat

 

PZT Centre, Armament Research & Development Establishment, Pune

 

Sintering of iron doped lead zirconate titanate (PZT) was studied by using microwave furnace. Microwave sintering was carried out in a multimode cavity at 2.45GHz. It was observed that samples could be sintered as low as 900^oC in microwave as compared to conventional sintering (>1200^oC). Thermal runaway was not experienced at high temperature. Microwave heating showed enhanced densification and reduced sintering time. Scanning electron micrographs reveal the fine and uniform grain size of the sintered samples. Microwave sintered samples showed no conductivity during poling.   Piezoelectric and dielectric properties were investigated and compared with conventionally sintered samples.

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PA-24                                                                                                              184

MARKET POTENTIAL OF FERROELECTRICS

Akhilesh Saurikhia* and Ambrish Saurikhia**

* Coordinator, Association for Sustainable Development, Modinagar

**Central Road Research Institute, New Delhi

Behaviour of ferroelectrics with respect to an electric field is analogous to
that of ferromagnet in a magnetic field. Their static dielectric constant
changes with temperature. They possess spontaneous electric polarisation in
temperature range of t < tc. Ferroelectrics exhibit stresses under action of
alternating voltage much like BH curve of ferromagnetic materials. Barium
titanate and Rochelle salt are familiar ferroelectrics. High dielectric
constants of ferroelectrics make them commercially important in manufacturing
small size capacitor of high capacitance. Their properties suggest their use
as memory devices for electronic computers. Piezoelectric acoustic
transducers and pyroelectric infrared detectors are other devices based on
ferroelectrics. Ferroelectrics play their role to land specific attribute to
the electric flow. Market for any component or product depends on variety of factors. Usage of a component is primarily defined by its properties in use. Then comes host of other factors, though detrimental to be selected for final usage. These may be the reliability of the component during the usage span, span of reliable working, management of problems, ability to be repaired or replaced,
integration of the component with the available technology, etc. Technology
has a cruel aspect too. With the advent of a new technology, the old one
becomes obsolete and gets replaced. The quickness depends on the magnitude of
advantages dispensed by the new technology. Economic difference between the
two is the biggest motivator. Generally, the new technology in one area is
coupled with advances in other areas related to the final product being
delivered. Advances in different areas are to be matched in the final
component and with the available technology. Thus the new product gets more
advantage over its predecessor. Ferroelectrics and the related research are also influenced by the market variables. This paper discusses the market potential of ferroelectrics including their raw materials. Market of any item is a very dynamic concept and hence any future advancement including research could affect the product, the research or the market itself.

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PA-25                                                                                                              07

EFFECT OF Ta SUBSTITUTION ON THE STRUCTURAL, DIELECTRIC, ELECTRICAL PROPERTIES OF Sr₅RTi₃Nb₇O₃₀ (R = Nd, Sm and Gd) FERROELECTRIC CERAMICS

 

M.R.Ranga Raju, R.N.P.Choudhary* and H. R. Rukmini

 

Department of Physics and Meteorology, I. I. T. Kharagpur

crnpfl@phy.iitkgp.ernet.in

 

The rapid technological advances along with faster and efficient communication system have not only opened up plethora of opportunities for engineers and scientists but also thrown up immense challenges in various fields of science and engineering. Extensive research over the years in physics and chemistry of solids has paved way for greater understanding of properties of solids. A larger section of material scientists are involved in research and development of ceramics for device applications namely sensors, actuators, computer memory and display, microwave devices etc. In this regard mixed oxide ceramics have always been an attractive proposition. Among the four types of materials belonging to ferroelectrics, the second largest used ferroelectrics next to perovskite-type is tungsten-bronze (TB) type ferroelectrics. They were important since there is a scope for different cations substitution among the available many interstitial sites i.e. A1, A2, C, B1 and B2 to vary the properties according to the requirement. Hence we, prepared polycrystalline Sr₅RTi₃Ta₇O₃₀ (R = Nd, Sm, Gd) compound by high-temperature solid-state reaction technique. The detailed characterization of these compounds over a wide range of temperature (150 – 700 K) and frequency (100 Hz – 1 MHz) using the complex impedance spectroscopy technique (CIS) show some important properties, which have potential applications for microwave devices. The effect of microstructure on the physical properties in these compounds is very interesting. The details of our study will be discussed.

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PA-26                                                                                                                       93

STRUCTURAL AND DIELECTRIC INVESTIGATIONS

OF La AND Pb DOPED SrBi₂Nb₂O₉ FERROELECTRIC

CERAMIC- A COMPARATIVE STUDY

 

Vaibhav Shrivastava, A.K.Jha^* and R.G.Mendiratta^#

 

Deprtament of Applied Physics, Delhi College of Engineering, Delhi-110042

#School of Applied Sciences, Netaji Subhas Institute of Tech., Delhi-110075

akjha@physics.dce.edu

 

In this paper, a comparative structural and dielectric study of Sr_1-xA_xBi₂Nb₂O₉ (A= La, Pb and x=0.1) ceramics is reported. The samples were synthesized using solid-state reaction method and were calcined and sintered respectively at temperatures 900 ^oC and 1150 ^oC for 2 hours. It has been observed that the tetragonal strain increases due to the introduction of lead and lanthanum onto the sites of strontium. The undoped SrBi₂Nb₂O₉ sample shows a decrease in orthorhombicity compared to the lanthanum and lead added samples. A little decrease in Curie temperature is observed after introducing lead whereas a large decrease is observed after introducing lanthanum. In addition, broadening of dielectric peak is observed after introducing lanthanum while for lead introduced sample it sharpens. The introduction of lanthanum in SrBi₂Nb₂O₉ shows significant space charge polarization contribution to the dielectric constant whereas with lead it is almost negligible. The dielectric loss is reduced significantly after introducing lanthanum and lead both; and the loss values in lanthanum-doped samples are found to be almost double compared of those in lead- doped samples.

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PA-27                                                                                                                      81

A MIXTURE OF CaCu₃Ti₄O₁₂ AND B₂O₃ AS A SINTERING AID FOR LOW TEMPERATURE DENSIFICATION OF PZT

 

R.Mazumder, A.Seal, A.Sen*, H.S.Maiti

 

Electroceramics Division, Central Glass and Ceramic Research Institute,

196, Raja S.C. Mullick Road, Kolkata- 32, West Bengal, India

asen@cgcri.res.in

 

Lead Zirconate titanate of composition Pb(Zr_0.52Ti_0.48)O₃ [PZT], which is close to the morphotropic phase boundary, finds widespread applications in actuators, ultrasonic motors, piezoelectric transformers due to their superior piezoelectric properties. However, such composition requires sintering at a high temperature (>1250^oC) in a controlled atmosphere to contain lead volatilization. To get around the problem, different sintering aids have been tried by various workers. However, in most of the cases the electrical properties of such sintered ceramics degrade due to the presence of sintering aids. Different workers^1,2 showed that some perovskite type additives like BiFeO₃, Ba(Cu_0.5W_0.5)O₃, lead germanium oxide were effective for the lowering of the sintering temperature of PZT without degrading the dielectric properties. The recently discovered^3,4 giant dielectric material CaCu₃Ti₄O₁₂(CCTO) posses some interesting feature; its dielectric constant is very large(10000 for ceramics) and constant over a wide temperature range (100-500K) and also it has a low melting point(1100⁰C).

In the present investigation, it has been found that the sintering temperature of PZT can be reduced by CCTO and H₃BO₃ addition and at the same time the dielectric properties are also improved. A sintered density of 95% of the true density was obtained at 1000⁰C/2h for 1wt% CCTO and 1.5 wt% H₃BO₃ addition. The CCTO addition, either above or below 1 wt% showed an inferior densification. The CCTO addition also gave rise to a lower lead loss and dielectric constant showed a peak (820 at 1 kHz, which is better than PZT) at 1wt% CCTO and 1.5wt% H₃BO₃ addition.

References:

1. S.Chu, C.S Hsieh, J.Mats.Sci.Lett. 18(1999) 1295-96

2. T.Hayashi, T.Inoue, Y. Akiyama, Jpn.J.Appl.Phys 38(1999) part I No. 9B 5549-5552

3.A.P.Ramirez, M.A.Subramanian, M.Gardel, G.Blumberg, D.Li, T.Vogt, S.M.Shapiro, solid state communication 115(2000) 217-220

4. C.C.Homes, T.Vogt, S.M.Shapiro, S.Wakimoto and A.P.Ramirez, Science, 293 (2001) 673

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PA-28                                                                                                                   112

Processing and properties of

fine scale piezoceramics

 

A.R. James* and J. Subrahmanyam

Ceramics & Composites Group, DMRL, Kanchanbagh, Hyderabad-58

james@dmrl.ernet.in

 

Two compositions of soft PZT were chosen to synthesize in the form of fine grain ceramics. These were subjected to high-energy milling. The milling was done using tungsten carbide (WC) bowls and WC balls for 2h, 4h, 6h and 8h, respectively. 250ml bowls and 10 WC balls of 20mm diameter, each were used for the purpose. The powders were milled at 200 rpm for the aforementioned durations. Powders were also milled in agate bowls with YTZ balls of 3 mm diameter, of Tosoh Corp. (Japan). SEM images were taken to determine the particle sizes. The electron micrographs revealed the formation of agglomerates, in the case of longer milling times. In each case these were compared individually with data acquired using a HELOS laser diffraction analyzer with a commercial dispersant (RODOS).  These powders were used to prepare pellets for electrical property measurements. Pellets without any excess lead in the starting compositions were sintered at different temperatures in order to determine the optimal sintering temperatures. The fine scale piezo-ceramics could be sintered at temperatures considerably lower than the usual 1250^oC, resulting in phase pure PZT. Interestingly, sintering the powders milled for 8 h, at 1250^oC resulted in the Pb deficient pyrochlore phase of PZT. The dielectric, piezoelectric and ferroelectric properties of the ceramics prepared from fine scale starting materials will be presented.

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SESSION IV

PROCESSING & CHARACTERIZATION –II

Wednesday, November 24, 2004

11.15 A.M.   -    01.15 P.M.

                                                                            

I-09                                                                                         126

RAMAN SPECTROSCOPIC STUDY OF Ba SUBSTITUTED

Pb(Yb_0.5 B"_0.5)O₃ (B"= Nb, Ta) SYSTEM

 

V. Subramanian

Microwave Laboratory, Department of Physics, IIT Madras, Chennai-600 036.

manianvs@iitm.ac.in

 

Lead ytterbium niobate, Pb(Yb_0.5 Nb_0.5)O₃ (PYN) and lead ytterbium tantalate, Pb(Yb_0.5 Ta_0.5)O₃ (PYT)  belong to the group of lead based complex perovskites with highly ordered B-site cations.  PYN exhibits a sharp paraelectric (cubic, Fm3m)-antiferroelectric (orthorhombic, Pnam) phase transition at 310 ^oC and PYT shows successive phase transitions from paraelectric (cubic, Fmm) –antiferroelectric (monoclinic, Pbnm) at 285 ^oC and antiferroelectric- ferroelectric (monoclinic, Pbnm) at 166 ^oC. Substitution of Ba²⁺ in place of Pb²⁺ results in antiferro-ferro-relaxor ferroelectric transition. In both the systems, the observed dielectric response becomes increasingly diffused with increase in Ba²⁺ concentration and noticeable dielectric dispersion is also observed for x ³ 0.15. The diffuseness can be attributed to the presence of polar clusters with local structure distortions.  Raman scattering is the appropriate technique to get more insight into the local distortions present in these systems. Raman spectroscopy studies carried out on the solid solution series (Ba_xPb_1-x)(Yb_0.5 B^״_0.5)O₃ (B" = Nb, Ta), 0 ≤ x ≤ 0.3 are analysed in conjecture with the low frequency dielectric dispersion data.

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I-10                                                                                         138

DEVELOPMENT OF LOW PERMITTIVITY MATERIAL

USING FLY ASH

 

Kamal Singh, Tanveer Quazi, Shail Upadhyay and Pramod Sakharkar*

Department of Physics, Nagpur University, Nagpur-440033

*S.F.S. College, Department of Physics, Seminary Hills, Nagpur-440 006

 

 

Dielectric behavior of fly ash*, barium titanate and three composites (of different wt.% of fly ash and barium titanate) have been measured in the temperature range 30 – 200 ⁰C and frequency range 100 Hz –1 MHz.  It is observed that dielectric constant of fly ash and composite is low as compared to barium titanate. The low value of dielectric constant of composites as compared to barium titanate may be attributed to occupancy of iron from fly ash to titanium site of barium titanate. It is observed that the dielectric constant of composites is independent of temperature in entire range of temperature measurement.

*The fly ash used for in this work was collected from Koradi Thermal Power station, Near Nagpur, India.

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I-11                                                                                                28

MAGNETOELECTRIC PHENOMENON IN COMPOSITES

 

S.V. Suryanarayana

Materials Research Lab., Dept. of Physics, Osmania Univ.,Hyderabad-500007

svspd@yahoo.com

 

Some insulating materials exhibiting simultaneous ferroelectric and magnetic behavior would yield a measurable voltage output under the action of external magnetic field or induced magnetization under the action of external electric field. This phenomenon is termed as the magnetoelectric (ME) effect. The materials exhibiting ME effect are called ferroelectromagnetics or magnetoelctrics. Since, two functionalities-ferroelectricity and magnetism- are observable in the same material simultaneously such materials become good platforms for multifunctionality, there by it is possible to exploit these materials for applications. The ME output can be realized both in single-phase materials and in composites. With recent interest in Spintronics, the work on magnetoelctrics is attracting worldwide attention.  Magnetoelectric phenomenon in composites arises due to the product property obtainable when two participating phases are suitably combined and care is taken for their proper synthesis.  In two-phase composites, the participating phases are –Piezomagnetic and piezoelectric. In either of the phases, the ME output will be present.  It is observable only in the composite, due to transfer of the stress from piezomagnetic phase to the piezoelectric phase. The composites can be prepared either by solid state sintering of the individual phases or by preparing laminates of the two phases .The ME output is dependent on applied magnetic field and also the thickness of the constituents. We have recently carried out extensive studies on composites of Ferrite/PZT composites and laminates. In this talk a review of the work carried out on ME composites will be presented.

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O-07                                                                                              69

ELECTRIC AND DIELCTRIC   PROPERTIES   OF   STRONTIUM BISMUTH    NIOBATE   VANADATES (SBVN)

 

¹Murali.K, ^1,2Rai.K.N

¹Material Science Programme,²Materials and Metallurgical Engineering,

Indian Institute of Technology, Kanpur - 208016

 

Srivastava A.K., Ram Kishore

National Physical Laboratory, New Delhi-110012

 

Strontium Bismuth Niobate Vanadates, SrBi₂ (V_0.1Nb_0.9)₂O₉ (SBVN), were prepared by solid state reaction of powder mixtures of constituent oxides and sintering. The partial substitution of Niobium by Vanadium cations (10 at. %), exhibited single - phase layered perovskite structure. X-ray diffractometry (XRD) and electron microscopy techniques were employed to examine the structure and microstructure of as produced material. The influence of vanadium doping on the structural and dielectric properties of Strontium Bismuth Niobate (SBN) was studied. These properties of SBVN were investigated in a range of temperatures (300 to 600 ^oC) and frequencies (50 Hz – 100 KHz). The incorporation of Vanadium into the layered perovskite structure resulted in a shift of the Curie point to higher temperatures from 435 to 460 °C. The DC and AC conductivity (100 KHz) of ferroelectric has been measured in the 300 – 600 ^oC temperature range by using impedance analyzer. A correlation of microstructural features with electric and dielectric properties of these materials has been discussed.

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O-08                                                                                        03

EFFECT OF MOLECULAR WEIGHT ON DIELECTRIC PROPERTIES OF POLYVINYL ALCOHOL (PVA) FILM

 

Girish Mukundra Joshi

 

Faculty Engg. Physics, Watumull Inst.of Tech., 47 R.G.Thadani Marg, Mumbai18

gm_joshi@rediffmail.com

 

Impedance analysis is the best technique to revel the micro structural details of the polymeric material. The dielectric polarization not only depends on physical and chemical properties but also on the degree of polymerization of the polymeric material. In the present study to understand the polarizing mechanism, two different molecular weights of polymer polyvinyl alcohol (PVA) used in the film form. Along with the various electrical parameters major focus was given to find out the dielectric properties of PVA film. All the measurements were carried out at NTP condition by LCR-4282A Impedance analyzer; in frequency range 20Hz to 1MHz for various DC bias potential from 0 to 40 volt. The result shows higher magnitude of dielectric constant for low molecular weight of PVA film in compar- eison to higher molecular weight, which is based on Maxwell-Wagner theory. 

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O-09                                                                                               78

TRANSPORT PROPERTIES OF POLYANILINE-

BaTiO₃ COMPOSITES

 

Syed Khasim,M V  Murugendrappa, K Sangshetty & M V N Ambika Prasad^#

 

Department of Physics, Gulbarga University, Gulbarga- 585 106

Prasad1_Amb@rediffmail.com

 

Insitu polymerization of fine graded BaTiO₃ powder (750nm) in polyaniline is carried out to synthesize polyaniline- BaTiO₃ composites with different weight percent of BaTiO₃ (10, 20, 30, 40 and 50) in polyaniline. The composites were characterized by SEM, XRD and IR spectroscopy to understand the formation of composites at molecular level. Transport properties such as ac and dc conductivities were measured and analyzed. It has been observed that both ac and dc conductivities increases up to 30 wt% of BaTiO₃ in polyaniline and decreases thereafter. Dielectric constant and Dielectric loss were also measured in these composites, in both the cases the values decreases up to 30 wt% of BaTiO₃ in polyaniline and increases thereafter. The observed behavior is due to increased chain length of polyaniline and obeys percolation theory.

Ferroelectric response of these composites were also studied, the composites with 30, 40 and 50 wt% of BaTiO₃ in polyaniline exhibited remarkable ferroelectric response. Because of electrical conduction of polyaniline and ferroelectric properties of BaTiO₃ these composites may find extensive applications. In microwave frequencies these composites behaves as lossless materials hence can be used as microwave absorbing materials.

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PA-29                                                                                                                   130

GROWTH AND CHARACTERIZATION OF PURE

AND LEUCINE DOPED FERROELECTRIC

TRIGLYCINE SULPHATE SINGLE CRYSTALS

 

C. M. Raghavan, R. Sankar, R. Jayavel

 

Crystal Growth Centre, Anna University, Chennai-600 025.

 

Triglycine sulfate (TGS) is one of the most studied ferroelectric materials. The interest in studying the growth and properties of pure and doped TGS crystals has been increased due to their effective application in various infrared-detecting devises.  TGS possesses monoclinic structure below and above the Curie temperature (49^oC).  The amino acids, l-leucine and isoleucine doped triglycine sulfate crystals have been grown from aqueous solution by slow cooling technique.  Bulk crystals were grown from a spontaneously nucleated seed by adapting a slow cooling rate of 0.01^oC per day.  The crystal morphology and properties are very much influenced by amino acid doping   

The morphology of pure, leucine and isoleucine doped TGS crystals shows that the degree of asymmetry in (010) and (021) plane is higher in both leucine and isoleucine doped TGS crystals. The (101) and (10 Ī) planes were well developed in the doped crystals whereas (001) and (00Ī) planes disappeared.  From the variation in morphology, it may be presumed that the surface diffusion enhanced in the leucine and isoleucine doped TGS crystals. The lattice parameter values were estimated by powder X-ray diffraction analysis and the significant change in lattice constant and cell volume confirm the presence of amino acids in the doped crystals. FTIR analysis qualitatively confirms the presence of the amino acids in the grown crystal.    AFM studies on the b-cut cleaved plate were carried out to observe the surface features and the domain structure. In the cleavage plane the appearance of layer pattern confirms the layer growth mechanism. 

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PA-30                                                                                                                     152

STUDY OF HYSTERSIS CURVE LOOP OF FEROELCTRICE CRYSTAL USING  MULTIFUNCTIONAL DIO CARD

 

H.V. Twari, Namita Agarkar, Om Prakash Basant

 

SOS in Electronics,Pt. Ravishankar Shula university,Raipur (C.G.)

 

A circuit is designed for tracing the hystersis loop for ferroelectrics crystal using DIO card on computer which is helpful to measure the variation of all ferroelectrics parameter by applying 50Hz sinusoidal electric field 2Kv,4Kv/cm with various magnitude (Em).

Such as spontaneous polarization (ps), Remanant polarization (Pr)  coercive field                      (EC), transition temperature (Tc) nature of phase transition order etc. this phenomenon was explained qualitatively using Weiss’s theory and software based on this was developed. The performance of the circuit and formulae developed are checked by various measurement on ferroelectrics tri glycine sulphate (TGS) pure and doped crystal with field and temperature.

 

 

Reference:

1.         The Handbook of personal computer instrumentation for data, cquisition test

measurment and control II ED. Burm-Brown coopration (1987).

2.         “Graphics programming in C”, Roger T. Stevens, BPB publication (1993)

3.         Dynalog  India PCL 812 card operation manual

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PA-31                                                                                                                     178

EFFECT OF LEAD IMPEDANCE ON

DIELECTRIC MEASUREMENTS

 

P. P. Anand*, Rajbir Singh*, V. K. Agarwal**

 

*Physics department, Meerut College, Merrut

**Physics department, CCS University, Meerut

 

Due to lead impedance, complex permittivity begins to show higher values at higher frequencies. This phenomenon has to be corrected before dielectric peak analysis has to be attempted. Lead impedance was considered as series combination of resistance and inductance

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PA-32                                                                                                                     182

MICROSTRUCTURE DEPENDENT DIELECTRIC PROPERTIES OF BaTiO₃  AND (Ba_0.5Sr _0.5)TiO₃ CERAMIC

 

P.V.Chandra Sekar, K.C.James Raju*,  M.Ghanashyam Krishna, 

and Anil. K.Bhatnagar

 

School of Physics, University of Hyderabad, Hyderabad. India

kcjrsp@uohyd.ernet.in

                                                            

In this work, effect of microstructure on the dielectric properties of Barium Titanate (BT) and Barium Strontium Titanate (BST) ceramics are investigated. They were prepared by the conventional solid-state reaction method. The pellets of these ceramics were given various heat treatments (1200^oC-1400^oC) to obtain different microstructures. The densification processes of the samples were followed at different sintering temperature and time. The dielectric properties were studied as a function of temperature, at lower frequency (2KHz-20KHz) by LCR meter (FLUKE PM 6304) and at higher frequencies (up to 100MHz) by using Agilent 4294 A Impedance Analyzer. The effects of grain size and crystallite size on the frequency dependent dielectric properties of the ceramics were studied. It is found that T_c, dielectric constant and loss at T_c, the Curie-Weiss constant, the Cole-Cole plot, the relaxation times etc of the ceramics are strongly microstructure dependent. These variations are explained in terms of both intrinsic and extrinsic effects. Porosity correction was applied for the measured dielectric constant values. XRD and SEM have been used for structural and microstructure analysis.

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PA-33                                                                                                                   155

TAILORING THE MICROWAVE DIELECTRIC PROPERTIES OF Ba(Mg_1/3Ta_2/3)O₃ CERAMICS

 

K. P. Surendran and M. T. Sebastian

 

Ceramic Technology Division, Regional Research Lab., Trivandrum-695 019

mailadils@yahoo.com

 

Dielectric Resonators represent a new series of versatile solid-state components, which revolutionized the microwave communication industry by replacing the bulky metallic cavities and microstriplines due to their unique selectivity and adaptability in microwave integrating circuits. These nonmetallic ceramics have high dielectric constant, low dielectric loss and high stability with temperature. Complex perovskite  Ba(Mg_1/3Ta_2/3)O₃ [BMT] is considered as ideal for dielectric resonator applications since they possess the highest reported Q factor in microwave frequency range. BMT is usually synthesized through solid state reaction technique and the sintering performed at high temperatures. But the satellite phases such as Ba₅Ta₄O₁₅, BaTa₂O₆, Ba₄Ta₂O₉ etc. formed during this procedure must be controlled to achieve high Q phase of BMT. Annealing at appropriate temperatures, relieves lattice strain and promotes the 1:2 cation ordering between Mg²⁺ and Ta⁵⁺. The increase of ordering parameter increases the material’s quality factor. Additives like Sb⁵⁺, Mn²⁺, Sn⁴⁺, Zn²⁺ and W⁶⁺ improve the microwave dielectric properties of BMT. These additives suppress the formation of secondary phases and promote better densification. Doping BMT with Zr improves Q factor, promotes the phase transition to a disordered 1:1 phase which poses serious doubts about the correlation between structural ordering and microwave quality factor. A slight percentage of non-stoichiometry favours the densification mechanism through lattice defects and improves microwave properties. Some glasses like ZnO-B₂O₃-SiO₂,_­ 5ZnO-2B₂O₃, ZnO-B₂O₃, B₂O₃ etc. lower the sintering temperature of BMT from 1650^oC to 1300^oC without sacrificing its dielectric quality factor. These glasses, which do not form intermediate phases with the matrix can be used as ideal liquid phase sintering medium in developing Low Temperature Co-fired Ceramics (LTCC) using BMT.  

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PA-34                                                                                                                     165

OPTICAL AND DIELECTRIC STUDIES ON SOL GEL DERIVED Pb_xCa_1-xTiO₃ CERAMICS

 

Arun Kr. Singh Chauhan, Vinay Gupta and K. Sreenivas

 

Dept. of Physics and Astrophysics, University of Delhi, Delhi-110007

arunatdu@hotmail.com

 

Sintered ceramic powders of calcium doped lead titanate [Pb_1-xCa_xTiO₃] ceramics with different Ca dopant concentration in the range (x = 0 to 0.35) have been prepared using a sol-gel technique. X-ray diffraction and Raman spectroscopy studies have been carried out to identify the phase formation. The infra-red absorption spectra in the mid-IR region (400 to 4000cm^-1) show the band corresponding to the Ti-O bond, which appears at 576 cm^-1 to shift to a higher wave number 592 cm^-1. The dielectric properties as a function of frequency, and phase transition studies on sintered ceramic Pb_0.65Ca_0.35TiO₃ has been studied in detail over a wide temperature range (30 to 600^oC) and the results are discussed.

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PA-34                                                                                                                   170

DEPTH PROFILING STUDIES OF TANTALUM OXIDE-TANTALUM INTERFACE BY X-RAY PHOTOELECTRON SPECTROSCOPY

 

Himani Sharma^1,2, G.S. Singh², Manika Khanuja^1,3 B.R. Mehta³

and S.M. Shivaprasad^1*

¹Surface Physics & Nanostructures, National Physical Laboratory, New Delhi

²Dept. of Chemistry, Delhi University, Delhi

³Dept. of Physics, Indian Institute of Technology, New Delhi

prasad@mail.nplindia.ernet.in

 

A X ray Photoelectron Spectroscopy study of the tantalum / tantalum oxide is reported. The native oxide of the polycrystalline Ta sample is probed for its interface behaviour by observing the core level, valence band and secondary electron emission spectra.  The Ta(4f) core level spectra of the native oxide shows two spin-orbit split peaks at 27.5 and 29.3 eV binding energies. 4KeV Ar⁺ ions are used to sputter the oxide surface layer by layer and the core level and the valence band are probed as a function of sputtered depth. A plot of the Ta/O XPS signal ratio versus the sputtering time shows that there is a stable phase with a Ta/O ratio of about 3 initially, upto a sputtering time of about 25 mins. After that the ratio increases monotonically until the oxygen peak almost disappears. Deconvolution of the XPS core levels in to Guassian components show the evolution of the pure Ta surface after sputtering In this region the Ta(4f) core-level spectra shows a significant shift in the spin orbit split peaks with the formation of an another pair of Ta (4f) peaks at 22.5 and 24.3 eV related to metallic Ta appearing. The oxygen deconvolution studies of the native surface show that in the native sample, two peaks of oxygen are seen at 531.0 and 534.1 eV and later reduces to only one peak at 531.0 eV. The change in work function through the interface is measured by observing the onset of secondary electron emission at the low kinetic energy region. The depth profiling shows the presence of atleast one stable Tantalum suboxide at the interface and increase in electron states at the Fermi level as elemental Tantalum is exposed after sputtering.

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PA-35                                                                                                                     175

HIGH RESOLUTION X-RAY DIFFRACTOMETRIC, PIEZOELECTRIC AND SPECTROSCOPIC STUDIES OF LiNbO₃ SINGLE CRYSTALS GROWN BY CZOCHRALSKI METHOD

 

G. Bhagavannarayana^a, K.K. Maurya^a, G.C. Budakoti^b and B. Kumar^b

^aMaterials Characterization Division, National Physical Lab., New Delhi-110 012.

^bDeptt. of  Physics & Astrophysics, Univ. of Delhi, Delhi-110 007.

 

LiNbO₃ single crystals grown by Czochralski (CZ) method were characterized in their as grown (in-situ poled), post-growth annealed and post-growth poled states by high-resolution X-ray diffractometry (HRXRD), piezometry, UV-Vis. and FTIR spectroscopy methods. From the diffraction curves, it was found that the as-grown specimens contain low and very low angle boundaries. Post-growth annealing at elevated temperatures results in removing the grain boundaries but leads to decrease in the piezoelectric constant d₃₃ showing misorientation of domains during annealing though the structural grain boundaries were removed. These samples were poled with different poling intensities. Poling on annealed specimens leads to enhancement in piezoelectric constant d₃₃.  The measured values of d₃₃ at poling fields 4, 6 and 8 kV/mm respectively are 16, 19 and 23 pC/N. The initial value of d₃₃ after annealing was only 14 pC/N. To see the homogeneity of Li content through out the crystal boule, different samples cut perpendicular to the growth direction from top to bottom along a length of two inches were studied by UV-Vis. spectra. Li content calculated by measuring wavelength positions of absorption edges indicates Li deficiency and its content is slightly varying in the range between 48.38 to 48.51 mol% respectively from bottom to top though the starting material has a Li content of 48.6 mol%.   Annealing and subsequent poling treatments lead to decrease of absorption coefficient and shifting of absorption edge. These results indicate the reduction of trace impurities and antisitic defects. FRIR measurements on post-growth annealed samples show significant reduction in OH^- concentration and almost complete removal of CO₃^2- ionic defects, which were otherwise observed in as-grown state.

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PA-36                                                                                                                       01

SYNTHESIS OF [(Ba_0.5Sr_0.5)(Ti_1-XZr_X)]O₃ CERAMICS: EFFECT OF Zr CONTENT ON DIELECTRIC PROPERTIES.

 

S.K.Rout and J.Bera*

P.G. Department of Physics, NIT

*Department of Ceramic Engineering, NIT, Rourkela-769 008

jbera@nitrkl.ac.in

 

Compositions in the system BaTiO₃-BaZrO₃-SrTiO₃ with varying Zr⁺⁴-concentrations were synthesized by solid oxide reaction route. Phase formation behavior was studied using TG/DSC and XRD. Investigation showed that the formation of (Ba_0.5Sr_0.5)TiO₃ was easier than (Ba_0.5Sr_0.5)ZrO_3­, which may be due to the presence of more acidic TiO₂ (than ZrO₂) in the earlier composition. XRD investigation showed that the composition forms cubic perovskite structure and lattice parameter increased linearly with the increase in Zr content due to the higher ionic radius of Zr⁺⁴ ion than Ti⁺⁴. Disc shaped samples were pressed uniaxially and sintered at 1400^OC for 12 hours for dielectric characterization. Bulk density, on an average, was found to decrease with the increase in Zr-content, mainly due to the increase in open porosity. But, the composition [(Ba_0.5Sr_0.5)Ti_0.6Zr_0.4]O₃ showed a very good densification having low porosity. Frequency dependence of room temperature dielectric measurement was carried out using HP 9142A LF impedance analyzer. Permittivity as well as dielectric loss decreased with the increase in Zr content except for the composition [(BaSr)Ti_0.6Zr_0.4]O₃ and they were very stable in the frequency range 100 kHz to 12 MHz.  The composition [(BaSr)Ti_0.6Zr_0.4]O₃ showed maximum permittivity as well as low loss factor among other Zr containing ceramics. Based on XRD analysis it may be concluded that the high permittivity was due to the presence of very fine crystallite size with defect crystal structure in the composition. That composition promises to show relaxor properties.

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PA-37                                                                                                                     132

strontium titanate ceramics prepared

from metallo- organic precursors

 

A.     Dhaneshwari Devi, H.B.Sharma, and H.N.K.Sarma

B.      

Department of Physics, Manipur University, Imphal-795003

hbsharma1@rediffmail.com

 

Ferroelectric strontium titanate (SrTiO₃) ceramics have been prepared by using metallo- organic precursors. Strontium acetate [Sr(CH₃COO)₂] and titanium (IV) isopropoxide [Ti (OC₃H₇)₄ ] were used as the precursors for the fabrication of the samples. The stock solution for the preparation of strontium titanate powder was prepared by dissolving strontium acetate in ethanol and acetic acid solvents and mixing the resultant solution with titanium (IV) isopropoxide in equimolecular amounts. The as fired powder was found to be amorphous. Annealing the amorphous powder at 700^oC for one hour in air yields cubic phase crystalline SrTiO₃ powder. Ceramic samples were prepared by pressing and sintering the crystalline powder. The effect of sintering temperature on the structural and dielectric properties were investigated and analyzed.

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PB-38                                                                                                                    104

DIELECTRIC CONSTANT OF RARE-EARTH COMPOUNDS

 

A.S. Verna, S.K. Rathi, D. Sharma and S.R. Bhardwaj

 

Department of Physics, B.S.A. College, Mathura-281004

In the present research paper an empirical relationship has been derived for dielectric constant determination of rare-earth susquioxide and rare-earth prictides (e.g. AXBY type compounds).  The proposed relation has been evolved in terms of average atomic number of constituent atoms (Zav).  A relationship between dielectric constant and average atomic number of contituent atoms is also discussed.  The trends observed in these two parameters reflect an inverse relationship.

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PB-39                                                                                                                      71

APPLICATION OF FERROELECTRIC TRIGLYCINE SULPHATE AS ALCOHOL SENSOR

 

Vasant Naidu, H. V. Tiwary *

 

*School of studies in Electronics Pt. Ravishankar Shukla Univ., Raipur–492 010,

Dr B. R. Ambedkar. Govt Polytechnic Pahargaon – 744103, Andamans, India

 

This is simple and highly sensing method for the determination and discrimination of alcohols at ppm level. This sensing is based on change in electrical conductivities and capacitance due to chemi-adsorption of alcohols at the surface of triglycine Sulphate(TGS) in a small duration of response time. This paper deals with the chemi-adsorption of alcohol vapours and give rise to the gas solid phase interaction with triglcine Sulphate pellet as the function of alcohol vapour concentration in air with its ambient leading to act as an alcohol sensor.

Keywords: Triglycine Sulphate, ferroelectric sensors, methyl alcohol and ethyl alcohol sensing.

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PA-40                                                                                                                       02

SYNTHESIS OF [(Ba_1-XSr_X)(Ti_0.5Zr_0.5)]O₃ CERAMICS: EFFECT OF Sr CONTENT ON DIELECTRIC PROPERTIES.

 

S.K.Rout, S.Panigrahi and J.Bera*

 

P.G. Department of Physics, NIT,

*Deptof Ceramic Engg., NIT, Rourkela-769 008

jbera@nitrkl.ac.in

Compositions in the system BaTiO₃- SrTiO₃- BaZrO₃ with varying Sr concentration were synthesized by solid oxide reaction route. Phase formation behavior was studied using TG/DSC and XRD. Investigation showed that the formation of Ba(TiZr)O₃ was easier than Sr(TiZr)O₃, which may be due to bigger particle size of SrCO₃. So the formation of BSTZ phase was controlled by the decomposition of SrCO₃. XRD investigation showed that the compositions formed cubic perovskite structure and lattice parameter decreased linerly with increase in Sr content, due to the smaller ionic radius of Sr⁺² than Ba⁺². Disc shaped samples were pressed uniaxially and sintered at 1400^OC for 12 hours for dielectric characterization. Bulk density increases with increase in Sr concentration mainly due to decrease in open porosity. Frequency dependence of room temperature dielectric measurement was carried out using HP 9142A LF impedance analyzer. Permittivity as well as dielectric loss decreased with the increase in Sr concentration. They were very stable in the frequency range 100 kHz to 12 MHz. However the composition [(Ba_0.2Sr_0.8 )(Ti_0.5Zr_0.5)]O₃ and Sr(Ti_0.5Zr_0.5)O₃ showed higher dielectric constant as well as low dielectric loss, may be due to the higher densification of the ceramics.

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PA-41                                                                                                                     110

STUDIES ON TUNGSTEN BRONZE BSLNN WITH

Dy³⁺ DOPANT CERAMICS

 

K.Chandramouli, P.Viswarupachary and G.Srinivasa Reddy

 

Solid State Physics and Materials Research Laboratories

Department of Physics, Andhra University, Visakhapatnam – 530 003

ckemburu@rediff.com

 

Tungsten Bronze Ferroelectrics which have a morphotropic phase boundary (MPB) can have a number of enhanced dielectric, piezoelectric, phyroelectric and electro optic properties compared to more conventional ferroelectric  materials.  The enhancement in physical properties is due to the proximity in free energy[1] of an alternate ferroelectric structure.  In the present work modified Barium Strontium Sodium niobate ceramics were processed by usual high temperature sintering technique and studied their dielectric properties near the MPB region.

The processed ceramic compositions are

1. Ba_1.6  Sr_2.4 Na₂  Nb₁₀  O₃₀
2. Ba_1.45  Sr_2.4  Dy_0.1  Li_0.2  Na_1.8  Nb₁₀  O₃₀
3. Ba_1.45  Sr_2.4  Dy_0.1  Li_0.4  Na_1.6  Nb₁₀  O₃₀
4. Ba_1.45  Sr_2.4  Dy_0.1  Li_0.6  Na_1.4  Nb₁₀  O₃₀
5. Ba_1.45  Sr_2.4  Dy_0.1  Li_0.8  Na_1.2  Nb₁₀  O₃₀
6. Ba_1.45  Sr_2.4  Dy_0.1  Li_1.0  Na_1.0  Nb₁₀  O₃₀

The values of the lattice parameters, cell volume, axial ratio and densities are calculated from the XRD Studies.  The computed values of the lattice constants obtained for the pure BSNN compositions are a=17.59A⁰, b=17.65A⁰ and c=3.93A⁰.    The experimental densities obtained in these compositions are about 95% to that of theoretical values.  From the computed unit cell volumes, it is found that there is no considerable change in the unit cell volume of Dy doped BSNN with increase of Lithium concentration.  The average linear particle size for all the compositions was estimated.  The dielectric studies as a function of temperature at 1 KH_Z frequency were carried out.  The dopant effect on the dielectric constant, dielectric loss and the ferroelectric phase transition temperature T_c is discussed.  D.C. resistivity studies are carried out as a function of temperature.  Resistivity studies indicated the PTCR response in these compositions.

References:

[1] Jaffe B.,Cook.W.R. & Jaffe.H, Piezoelectric Ceramics”,Academ.Press,NewYork, 1971

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PA-42                                                                                                                    124

DIELECTRIC PROPERTIES OF

COBALT SUBSTITUTED Li-Ni-Mn FERRITES

 

Mamata Maisnam, Sumitra Phanjoubam and H.N.K. Sarma

Department of Physics, Manipur University, Canchipur, Imphal-795003

 

L. Radhapiyari Devi, O.P. Thakur and Chandra Prakash

Electroceramics Group, Solid State Physics Laboratory, Delhi -110 054

sumitrap@sancharnet.in, prakash@ssplnet.org

 

Samples with compositional formula Li _0.45-x/2Ni_0.1Mn _0.1Co_xFe_2.35-x/2O₄ with x ranging from 0 to 0.1 in steps of 0.02 prepared by the conventional ceramic technique were investigated. The single phase spinel structure of the samples has been confirmed by XRD analysis. The lattice constant was observed to increase with increase of substitution. The dielectric constant and corresponding loss tangent were studied as a function of substitution level and frequency in the range 100Hz to 1MHz.  A decrease is observed in the value of dielectric constant with substitution. Dispersion in the dielectric constant with frequency is observed for all the samples. The frequency dependence of loss tangents shows resonance peak. The possible mechanisms contributing to the results have been discussed.

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PA-43                                                                                                                    115

SURFACE PLASMON RESONANCE : A TOOL

FOR INVESTIGATING METAL\DIELECTRIC INTERFACE

 

Rajni Mahajan   and  S.Annapoorni

 

Department of Physics and Astrophysics, Delhi University, Delhi-110007

rmahajan@ physics.du.ac.in

 

Surface Plasmon Resonance (SPR) is a general spectroscopic technique for sensing refractive index changes near the surface of a metal film. Its high level of sensitivity to these changes provides a versatile tool for the observation and the quantification of the reactions at the metal\dielectric interface. The generality of the technique has thereby led to its applications in a variety of systems including materials characterization, gas and chemical sensing, biosensing, surface enhanced Raman spectroscopy (SERS), non-linear optical thin films, self-assembled monolayers (SAMs)), fluorescence enhancement, Langmuir-Blodgett films, thin organic films at electrochemical interface etc.Surface plasmons are an interesting phenomenon that occurs in thin films of metals with a complex dielectric constant. Originating at the boundary between an insulator and a conductor, they can be described through many different formalisms. Mathematically, surface plasmon can be seen as a solution to Maxwell 's thin film equations at the boundary between an insulator and a metal.  Conceptually, they can be described as a charge density wave at the interface of an insulator and the metal. Surface plasmons can also be understood as a thin film interference effect, where the thin film has a large complex index of refraction.

SPR relies on the optical excitation of surface plasmons in a free electron metals (Silver, Gold). Back side, p-polarised illumination of a prism-coupled film at some angle greater than the critical angle for total internal reflection results in plasmon excitation at the metal\dielectric boundary. Plasmon excitation is observed as an increase in the optical absorbance (decrease in the reflectance) at an optimum coupling angle. This in turn results in a minimum in the SPR curve (reflectance Vs angle) which is referred to as the plasmon angle θp. Sensing via SPR is possible due to extreme sensitivity of θp to changes in the index of refraction near the metal surface brought by the adsorption, molecule-molecule interactions etc at the metal dielectric interface.  u

 

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PA-44                                                                                                                     117

STRUCTURAL, DIELECTRIC AND ELECTRICAL PROPERTIES OF KBa₂­­­X₅O₁₅(X=Nb and Ta) CERAMICS

 

Banarji Behera¹, P.Nayak¹ and R.N.P.Choudhary²

¹P.G.Deparrtment of physics, Sambalpur University, Burla, Sambalpur, India

²Department of physics and Meteorology, IIT, Kharagpur, India

 

Since the discovery of ferroelectricity properties in barium sodium niobates (BNN), a large number of niobate and tantalate compounds have been studied for some device application. Some oxides in ceramics and thin film form with tungsten bronze (TB) structure play major role in fabricating solid state devices, such as computer memory and display, pyroelectric devices, electro-optic devices etc. In view of the importance of new materials for device application, we have planned to study the structural, dielectric and electrical properties of KBa₂X₅O₁₅(X=Nb and Ta) ceramics [1,2]. Polycrystalline samples of KBa₂X₅O₁₅ (X=Nb and Ta) were prepared by using a high temperature solid-state reaction technique. X-ray diffraction pattern have been recorded in a wide range of Bragg’s angle 2(20⁰80⁰) with a scan rate of 3⁰ per minute. Preliminary structural analysis confirms the formation of the compound. Measurement of the dielectric constant and tangent loss as a function of frequency at different temperature have provided many interesting properties of the compounds. Electrical conductivity (dc) shows negative temperature co-efficient of resistance behavior.

 

References:

 

1.       E.A.Geiss, B.A.Scott, G.Burns, A.W.Smith, B.L.Olson and D.F.O’Kane.,  Mat. Res.Bulletin 5 (1969) 109-115.

2.   R.N.P.Choudhary, Ratnakar Palai and S.Sharma. Materials Science & Engineering B77 (2000) 235-240.

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PA-45                                                                                                                      16

EVANESCENT MICROWAVE PROBE STUDY ON SURFACE DIELECTRIC PROPERTIES OF MATERIALS

 

H.-F. Cheng¹, and Y.-C. Chen²

 

¹ Dept. of Physics, National Taiwan Normal Univ., Taipei 116, Taiwan, R. O. C.

² Dept. of Physics, National Cheng Kung Univ., Tainan 701, Taiwan, R. O. C.

 

A recently developed evanescent microwave probe (EMP) combined with systematically quantitative analyses is introduced in this study. The EMP measurement is based on the scanning-probe and the near-field techniques. Briefly, the system design consists of a sharp metal tip protruding through the end wall of a coaxial resonant cavity. The high spatial frequency components of evanescent waves generated at the tip is inversely proportional to tip radius and currently reach l/10⁵ on dielectric samples. However, due to the complexity of the near field distribution in the tip-sample region, it is difficult to obtain an analytical solution of the sample properties. To overcome this problem, we use a 3-dimensional (3D) finite element simulation and equivalent circuit to model the behavior of the electromagnetic fields inside the resonant cavity and near the tip. A modified analysis on sample quality factor, which is usually dominated by conductor losses of the resonator, is especially proposed. Experimental results on various dielectric samples are also performed to support the theoretical ones, which demonstrate that the analyses are useful for EMP study, and provide a way for surface dielectric imaging.

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SESSION V

PIEZOELECTRIC AND PYROELECTRIC

Wednesday, November 24, 2004

02.00 P.M.   -    03.30 P.M.

 

I-12                                                                                              127

MICROSTRUCTURE, FERROELECTRIC & PYROELECTRIC PROPERTIES OF EUROPIUM MODIFIED PZT CERAMICS

 

Seema Sharma* and T.C.Goel

 

Dept. of Physics, BITS-PILANI-GOA Campus, Zuarinagar-403726, GOA

seema_sharma26@yahoo.com

 

Electroceramics based on lead zirconate titanate (PZT) are widely used in various memory elements, pyroelectric and piezoelectric devices .  Depending upon the specific requirements for different applications of piezoelectric ceramics, various compositions of the PZT system may be chosen. Various modifications have been made with rare earth elements in order to improve the piezoelectric and pyroelectric properties. In the present work, an attempt has been made to understand the effect of different Eu concentrations in PZT system. Polycrystalline samples of Europium modified lead Zirconate titanate  has been prepared by high temperature solid state reaction technique. The structural characterization of the samples investigated by X-ray diffraction technique exhibit tetragonal structure. PEZT ceramics with 2% of Eu show single perovskite phase. Scanning electron micrographs show uniform, densely packed structure. Pyroelectric and Ferroelectric properties carried out on the samples have been reported and discussed. PEZT (2/55/45) show good current responsivity (Fi ), voltage responsivity (Fv ) and detectivity (F_d), in comparison to other compositions under study. Moreover its ferroelectric properties (high remanent polarization with low coercive field) make it suitable material for nonvolatile memory applications. 

Keywords: X-ray diffraction technique, Pyroelectric, Ferroelectric, Solid state reaction

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I-13                                                                                              187

IMPEDANCE AND PIEZOELECTRIC PROPERTIES OF

LEAD  POTASSIUM NIOBATE

 

K.Sambasiva Rao

Centre for Piezoelectric Transducer Materials, Dept. of Physics,

Andhra University, Visakhapatnam – 530003.

konapala@satyam.net.in

Mixing of two ferroelectric compounds, Lead Niobate (PbNb₂O₆) and Potassium Niobate (KnbO₃) in different proportions a whole set of materials, Lead Potassium Niobate (Pb_1-xK_2xNb₂O₆ - PKN­) can be obtained. The materiial PKN has limited solid solutions between the end members for x varying from 0 to 0.34. The present talk discusses the thermal, impedance, FTIR, Ferroelectric, Piezoelectric and X-ray analysis of the solid solutions of PKN for x = 0.20 – 0.34. Temperature response of real part of permitivity at several frequencies on the above compositions be presented. The results on the frequency dependence of real and imaginary parts of the impedance and corresponding organ diagrams obtained in the frequency range 10² – 10⁶ Hz be discussed. Thermal behaviour of AC conductivity in all the compositions be illustrated along with the piezoelectric properties. Absorbance nature of PKN was measured over the wavelength range of 0.5mm - 25mm by FTIR. Finally one of the compositions of PKN for x = 0.23 has been prepared through semi precursor method and performed the above properties and compared with the same material prepared by conventional ceramic route.

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O-10                                                                                               58

FERROELECTRIC AND PIEZOELECTRIC PROPERTIES

 OF THE CERAMIC  Pb₀.₇₆Ca_0.24Ti_(I-x) Nb_x/2 Cr_x/2O₃

 

A.P.  Kulkarni, S.A.  Pawar, N.T.  Padal, S.R.  Kokare  and P.B.Joshi

 

Department of Physics, Solapur University, Solapur- 413 255.

drpbjoshi@rediffmail.com

 

The ceramic Pb_0.76Ca_0.24Ti_(I-x)Nb_x/2Cr_x/2O₃  compounds  for  compositions  x=0.00,0.01,0.02,0.03,0.04  &  0.05  are  prepared  using  high  temperature  ceramic  synthesis  method.  The present paper reports investigations of relative permittivity Є_r along with complex impedance analysis, electrical conductivity σ, pyro-electric coefficient Φ. saturation polarization Ps and various piezo-electric coefficients and parameters e.g. d₃₃, d₃₁, K_p, N_p, Y^o_E etc_.   The observations on electrical permittivity Є_r are carried out both as a function of temperature  & frequency.  The results of all these investigations indicate the usefulness of this material as a pyroelectric sensor  & a low Qm piezoelectric transducer.  It is observed that the composition with x=0.04 has useful parameters for device applications.  The structural  & infrared studies of these compositions are also carried out.

The observations on electrical permittivity are analyzed in terms of the complex impedance data determined both below as well as above the curie temperature. The observed electrical permittivity has been separated out in terms of the grain and grain boundary contributions using a theoretical model. The grain boundary capacitance shows a behavior characteristic of an interfacial polarization, while the grain capacitance shows an existence of an intra-grain barrier layer. The analysis of the grain and grain boundary resistance, as a function of temperature are complimentary to the above-mentioned proposition.

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O-11                                                                                        109

PYROELECTRIC PROPERTIES OF POLYCRYSTALLINE

PBN COMPOSITIONS

 

K.Chandramouli, G.Srinivasa Reddy and P.V.Achary

 

Solid State Physics and Materials Research Laboratories

Department of Physics, Andhra University, Visakhapatnam – 530 003

ckemburu@rediff.com

                           

Ferroelectric Lead Barium Niobate (PBN) has recently regained its importance because it is a lead containing tungsten bronze type ferroelectric relaxor with a morphotropic phase boundary (MPB) and has potential in applications.  These tungsten bronze ferroelectric materials are found to be technologically important materials for device applications due to their high dielectric constant, Piezoelectric, Pyroelectric and electro optic properties.  The best known MPB system is lead barium niobate, PBN (Pb_1-x Ba_x Nb₂ O₆).  Preparation of dense ceramics and poling of PBN ceramics is some what difficult compared to other ferroelectric compositions.  The conventional ceramic method of cold pressing in a die punch assembly using a hydraulic press to compress into disc shape and sintering at 1290-1300⁰ C was adopted to process the poly crystalline materials, using the general formula of Pb_(x-3y/2) Ba_(1-x) Ce_y Nb₂ O₆. to yield the following compositions.

Pb_0.65  Ba_0.35  Nb₂  O₆

Pb_0.62  Ba_0.35  Ce_0.02  Nb₂  O₆

Pb_0.59  Ba_0.35  Ce_0.04  Nb₂  O₆

Pb_0.56  Ba_0.35  Ce_0.06  Nb₂  O₆

Pb_0.53  Ba_0.35  Ce_0.08  Nb₂  O₆

Pb_0.50  Ba_0.35  Ce_0.10  Nb₂  O₆

The temperature variation of dielectric measurements were taken using the digital L.C.R. meter gave the values of the capacitance with the help of which the dielectric constant of the prepared polycrystalline compositions were obtained. The Pyroelectric current was measured using the method of Byer and Roundy [1] and the Pyroelectric coefficient in the present  study was estimated. The temperature variation of Pyroelectric Coefficient for all the composition studied.  The values of Figure of merit are calculated.  The effect of cerium on Dielectric and Pyroelectric properties are discussed.

References:  1. R.L.Byer and C.B.Roundy, Ferroelectrics 3, (1972) 330.

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O-12                                                                                             125

BULK CRYSTAL GROWTH OF PIEZOELECTRIC

0.91PB(Zn_1/3 Nb_2/3)O₃-0.09PbTiO₃ BY BOTTOM COOLING  METHOD AND DOMAIN STRUCTURE STUDIES

                                                                       

S.V. Rajasekaran, S. Madeswaran and R.Jayavel

 

Crystal Growth Centre, Anna University, Chennai-600 025, India.

    

Piezoelectric single crystals of complex lead based perovskites with the general formula Pb(B₁B₂)O₃ (B₁=Mg²⁺, Zn²⁺, Ni²⁺, Sc³⁺, B₂=Nb⁵⁺,Ta⁵⁺, W⁶⁺) so called relaxors, which have rhombohedral (or) monolclinic structures posses tetragonal structure with lead titanate PbTiO₃(PT).  PT has the largest polarization among the perovskites and is an indispensable compound for obtaining large dielectric and piezoelectric properties. The solid solution of Pb(B₁ B₂)O₃-PT  has  morphotropic phase boundary (MPB), where  it shows considerable large electromechanical (e/m) coupling factors and dielectric constant.  Relaxor-PT materials are superior compared with conventional PZT by their good mechanical properties, reducing PbO evaporation during the firing process, synthesis of single crystals which show promising properties. The excellent piezoelectric properties make these crystals promising for medical ultrasonic, nondestructive testing and undersea application.

In the present study, high temperature solution growth technique by bottom cooling method was adopted to grow 0.91Pb(Zn_1/3Nb_2/3)O₃-0.09PbTiO₃ (PZNT-91/9) single crystals, which have  rhombohedral-tetragonal morphotropic phase boundary.  Processing conditions have been optimized during the growth of bulk crystal, including variation of flux-charge ratio, cooling rate, soaking period and growth temperature. The crystals were characterized by XRD structural analysis. The crystalline quality and orientation was confirmed by Laue pattern.  Chemical composition of the grown crystal was analysed by EDX.  Dielectric and domain structure of PZNT-91/9 single crystals have also been investigated.   

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PB-01                                                                                                                     157

PIEZOELECTRIC AND DIELECTRIC STUDIES ON SOL-GEL DERIVED NONSTOICHIOMETRIC SrBi₂Ta₂O₉ CERAMICS

 

Rajni Jain, Vinay Gupta, and K. Sreenivas

 

Department of Physics and Astrophysics, University of Delhi, Delhi-110007

 

The non-stoichiometric compositions of strontium bismuth tantalate (SBT) [Sr_1-xBi_2+2x/3Ta₂O₉] with x = 0.0, 0.15, 0.30, 0.45 has been prepared by sol-gel derived powders. The dielectric and ferroelectric properties of SBT ceramics are found to improve with increase in x up to 0.3, and degrade beyond x>0.3 due to limited solid solubility in the SBT system. Poling treatment reduces the dielectric dispersion and dielectric loss in the frequency range (0.1 to 100 kHz). The resonance and anti resonance frequencies increase with increase in x (x=0 to 0.30), and the corresponding minimum impedance decreases. The electro mechanical quality factor (Q_m) shows a maximum value of 915 for SBT composition with x=0.30. The measured coupling coefficients (k_p) are small (0.096 to 0.100) for x = 0 to 0.30.  The values of piezoelectric charge coefficient (d₃₁) and piezoelectric voltage coefficient (g₃₁) are estimated. The positive values of d₃₁ and g_31, and the low dielectric permittivity of SBT yield a high value for hydrostatic coefficients, despite the low charge coefficient (d₃₃=24pC/N). The maximum values of charge coefficient (d_h=34 pC/N) and voltage coefficient (g_h=39 x10^-3 Vm/N) are obtained for x=0.30, and the estimated hydrostatic figure of merit (=1215) is high.

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PB-02                                                                                                                     148

STRUCTURAL CHARACTERISTICS OF QUARTZ CRYSTALS AND THEIR ROLE ON OSCILLATOR PERFORMANCE

 

Harish Bahadur* and R.P. Tandon**

 

*National Physical Laboratory, Krishnan Road, New Delhi.

** Department of Physics and Astrophysics, University of Delhi, Delhi

 

Quartz oscillator crystals are used for a variety of technological applications. The frequency of thickness-shear mode quartz crystal oscillator in rotated Y-plates and similar crystals is given by f = n/2t (cN/D) ^½where n is the overtone number, t is the thickness of the crystal, D  is the density, and  c!  is the rotated elastic modulus. The elastic modulus and the density are the primary materials factors that determine the crystal frequency. Other factors such as piezoelectric coupling, resonator contour, and mounting structure also play a role in the actual frequency of the quartz device. The elastic modulus represents a type of average of the interatomic force constants. Thus, it should be sensitive to the substitution and /or modification of impurities and defects in the crystal lattice.   Point defects  are of  atomic size  and  play a very crucial role in the application of a  quartz as a device. The Q (or the Quality Factor) of a quartz resonator directly depends on the type and concentration of impurities introduced in the material during its growth. These impurities are randomly distributed in the crystal. It thus becomes important to develop cleaner growth procedures and improved screening tests to evaluate the crystal for its quality. It is expected that through a greater understanding of the relationship between structural characteristics or specific defects and the performance of a quartz device, it would be possible to make a superior quartz for a specific application.

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PB-03                                                                                                                     166

PROCESSING AND DIELECTRIC & PIEZOELECTRIC PROPERTIES OF OXIDES AND SOL-GEL POWDER DERIVED PMNT CERAMICS

 

Pawan Kumar¹, R. Chatterjee¹, O. P. Thakur², C. Prakash² and T. C. Goel³

 

¹Department of Physics, Indian Institute of Technology, New Delhi-110016, India

²Electro-ceramics Group, SSPL, Lucknow Road, Timarpur, Delhi-110054, India

 ³BITS  Pilani - Goa Campus, Zuari Nagar-403726, Goa

CHANDRA_PRAKASH/SSPL@ssplnet.org

 

Recently, a great deal of interest has focused on relaxor ferroelectric materials due to their excellent piezoelectric, strain induced by electric field and dielectric properties. Lead magnesium niobate (PMN) forms a solid solution with lead titanate (PT) denoted as PMNT. PMNT compositions close to the morphotropic phase boundary (MPB) exhibit enhanced electromechanical and electrostrictive properties with a very high piezoelectric constant. PMNT 68/32, a MPB composition, has been prepared in bulk form using oxides and sol-gel derived powder as starting materials. In both the cases, perovskite structure was formed at 700^oC calcination temperature. Room temperature value of dielectric constant(e_r) and dielectric loss (tand) at 1kHz were found to be ~ 2100, 0.065 and 2800, 0.04, respectively, for the oxides and sol-gel derived PMNT 68/32 ceramics. Presence of butterfly shaped loops confirms the piezoelectric nature of the samples. Strain vs. unipolar electric field, S-E, behavior shows the development of ~0.19 and 0.5% strain with strain hysteresis ~2 and 20% in oxides and sol-gel derived ceramics, respectively. Piezoelectric coefficient, d₃₃, calculated from the S-E behavior is found to be ~290 and 550pm/V, respectively, for oxides and sol-gel derived samples. Development of high strain with low hysteresis in oxides derived ceramics suggests its suitability for actuator applications.      

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PB-04                                                                                                                     149

CHARACTERIZATION OF ELECTRODE MATERIAL OF QUARTZ RESONATOR OF QUARTZ CRYSTAL MICROBALANCE

 

V.K. Hans*, Mahesh Kumar*, S.M. Shivaprasad*, Harish Bahadur*,

K.N. Sood*, Ram Kishore*, Prabhat K. Gupta* and S.C. Garg*

 

*National Physical Laboratory, Dr. K.S.Krishnan Road, New Delhi

 

The major stimulus in research in quartz crystals has been largely due to the varied technological applications for which quartz is uniquely suited, such as  in optics,  clocks for microprocessors,   temperature and  mass sensors, accelerometers and a variety of  electronic devices including crystal oscillators and filters for precision frequency control, communications and generally in signal processing in computers. Recent development of Quartz Crystal Microbalance (QCM) has added a new dimension to the application of quartz crystals wherein almost every conceivable aspect in the analytical measurements can be performed by using a quartz crystal resonator.   

We present our studies on analysis of a quartz resonator used in the QCM using  XPS, Scanning Electron Microscopy results of the electroded portion of quartz resonator. The analysis was done by the the XPS system of Perkin-Elmer Model 1257, which consists of a dual anode (Mg K"/Al K") X-ray source and a 285 mm radius, high resolution Hemispherical Electron Energy Analyzer. The sample under analysis was mounted on a high precision x, y, z, 2 manipulator inside a UHV chamber of base pressure 5 x 10 ^-10 Torr. The XPS analysis was done by a 15 kV, 100W, MgK" source, and the secondary electrons emitted were analyzed with the analyzer normal to the sample surface. The low resolution survey scans and high resolution core level spectra were taken with pass energy of 100 eV and 40 eV respectively. The surface was sputtered by using differentially pumped Ar⁺ ion source of 40 KV at an etch rate of approx. 10D per minute. The results showed peaks of Ni, Co, Fe, Ag, and C. The peaks of Fe and Co were that of the sample holder. The peak for Ag is supposed to be due to the silver paste used in mounting the resonator for contacts. The sample was then sputtered by Ar⁺  ion source of 4 KV at an etching rate of 10D/minute/FA, for 5 min at 2FA (this approximates to about 100D). The position of the sample was shifted to new position for XPS, so that all the X-rays were falling on the contacts of the sample. It was found that all the contamination (Carbon and Oxygen) on the surface was removed and it is concluded that the sample surface after sputtering was entirely made of Ni and no other trace of elements was found on the surface. Microstructural and EDS analysis have also been presented. The results would find application in developing QCM.

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PB-05                                                                                                                     185

AC CONDUCTIVITY IMPEDENCE AND PIEZOELECTRIC PROPERTIES ON PRESEODYMIUM MODIFIED PBKNN

 

K.Sambasiva Rao, N.Vallisnath and P.Murali Krishna

 

Centre for Piezoelectric Transducer Materials, Dept. of Physics

Andhra University, Visakhapatnam – 530003.

konapala@satyam.net.in

 

The binary (1-x) Pb₂KNb₅O₁₅ (PKN) – xBa₂NaNb₅O₁₅ (BNN) – (PBKNN) has a MPB region at x = 0.25. The present paper gives the preparative conditions, structure, micro structure, dielectric, ferroelectric, piezoelectric, pyroelectric thermal AC conductivity impedance and absorbance studies on solid solutions of Pb_2-2x-3y/2Ba_2xPr_yK_1-xNa_xNb₅O₁₅ where x = 0.20, 0.25 and 0.30 and y = 0.00 and 0.05. The compositions are characterized to be orthorhombic. Substitution of Preseodymium (Pr) inhibited the grain growth of PBKNN. One of the Pr – PBKNN composition whose spontaneous polarization value has been observed to be 69.68µC/cm² much larger than the corresponding composition of unsubstituted PBKNN. Substitution of Pr decreases the value of transition temperature of PBKNN. The piezoelectric constants K_p, K_t, K_31, d_31, g₃₁ and S^E₁₁ of Pr – PBKNN have been found to be larger than unmodified PBKNN. The room temperature pyroelectric coefficient 0.56 x 10^-8 C/cm^2oc in one of the Pr – PBKNN composition has been found, the value is much larger than PBKNN. The results of thermal AC response of conductivity, impedance, absorbance FRIT (0.5 µm – 25 µm) in all the compositions be presented.

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PB-06                                                                                                                     186

ELASTIC PIEZOELECTRIC AND PYROELECTRIC STUDIES

OF YTTRIUM MODIFIED PBN

 

K.Sambasiva Rao, N.Vallisnath and P.Murali Krishna

 

Centre for Piezoelectric Transducer Materials, Dept. of Physics

Andhra University, Visakhapatnam – 530003.

konapala@satyam.net.in

 

PB-07                                                                                                                       24

Dielectric and piezoelectric properties

of ( Na_1-x  K_x )_1/2Bi _1/2TiO ₃

 

P. Vijaya Bhaskar * and T. Bhima sankaram

 

 Materials Research Lab., Dept. of Physics, Osmania Univ., Hyderabad 500007

poluri_vijay@rediffmail.com

 

Lead oxide based piezoelectric exhibit some of the highest field induced strains and good electrical –mechanical energy of known compounds but the toxicity and high vapor pressure during the processing of lead oxide ceramics have resulted in an increasing demand for environmentally safer alternative materials with comparable properties. The present report confines to the work on the mixed (Na_1-x K_x )_1/2 Bi_1/2TiO₃ system with x =0.1, 0.15, 0.2, 0.3.  The ceramic is have been prepared by conventional double sintering process. The lattice parameters have been determined by x-ray diffraction. The dielectric property has been studied as a function of temperature (RT to 600 ^oC) and frequency (10 KHz – 1MHz).  The electro-mechanical coefficients have been measured by Resonance Anti-Resonance method. The results are presented. The DC conductivity has been studied for the samples. The activation energies have been calculated from the data.

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PB-08                                                                                                                     162

CORRELATION OF MICROSTRUCTURE WITH DIELECTRIC PROPERTIES OF MODIFIED PZT

 

Sukhbir Singh¹,T.D. Senguttvan¹, V. S. Pawar² and R. P. Tandon³

 

¹Scientist, National Physical Laboratory, New Delhi – 110 012

²Ex-Scientist, National Physical Laboratory, New Delhi – 110 012

³Department of Physics and Astrophysics, University of Delhi, Delhi – 110 007

 

Lead zirconate titanate (PZT) ceramics are materials of great industrial applications. These include  use in many underwater acoustic devices, ultrasound, biomedical imaging, smart material, MEMS devices and new generation of ferroelectric memories  for computer applications. Usually undoped PZT materials do not possess favorable properties for specific applications. However, they can be tailored to suit particular applications by the use of suitable modifiers. In the present case we have investigated the role of Lanthanum and Samarium oxides on the dielectric and piezoelectric properties. Samples were fabricated by solid state reaction, followed by the sintering at 1250 ⁰C of the compacted samples. X-ray were used to confirm the presence of desirable phase and the microstructure was examined under SEM. The density of sintered samples of La and Sm doped samples ranged between 7.80 to 7.92 x 10³ Kg m^-3. Typical grain size for Sm (1 mol%) was about 2 m which increased to 7-8 mm when Sm was increased to 3 mol%. Similar quantitative behavior was seen for La doped samples. Both these modifiers had significant influence on enhancing the piezoelectric coefficient (d₃₃) A maximum value of about 300 pCN was achieved for Sm₂O₃ and 380 pCN for La₂O₃ doped samples. Sm₂O₃ addition seem to improve the piezoelectric coefficient (g₃₃) considerably which would be useful for their application in ultrasonic detection.

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PB-09                                                                                                                    164

ROLE OF LANTHANUM ADDITION ON THE GRAIN SIZE AND PIEZOELECTRIC BEHAVIOR OF PbTiO₃ CERAMICS

 

M.R.Tripathy¹,Ajay K. Arora², S.Tandon³ and R.P.Tandon*¹

 

¹Department of Physics and Astrophysics, University of Delhi, Delhi – 110 007

²Keshav Mahavidyalaya, University of Delhi, Keshavpuram, Delhi – 110 035

³Deen Dayal Upadhyaya College, University of Delhi, Karampura, Delhi 110 015

*rptandon@physics.du.ac.in

 

Modified lead titanate ceramics were prepared using solid state reaction. A fixed amount of (1 mol%) iron (Fe) was added to get highly dense materials. Addition of 1 mol% Molybdium (Mo) promoted grain growth. Lanthanum (La) concentration was verified between 2 to 20 mol% and maintaining the concentration of Fe and W was pegged at 1 mol%. The Curies temperature and tetragonality decreased with increased La content. The dielectric constant exhibited a systematic increase with increasing La content. The piezoelectric coefficient was measured and it was observed that the thickness coupling coefficient (K_t) showed a substantial increase with increasing La content attaining a peak value  of 0.62 around 18 mol%. The planar coupling coefficient was almost independent of composition.

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SESSION VI A

THIN FILMS – PROCESSING & STUDIES

Thursday, November 25, 2004

09.00 A.M.   -    11.00 A.M.

 

I-14A                                                                                              75

MULTILAYER ELECTROCERAMIC THIN FILMS

 

D. C. Agrawal

 

Materials Science Programme, IIT Kanpur 208016, India

 

Thin film multilayers consisting of alternating layers of different compositions appear to be very promising for generating structures having unique combinations of properties. Several such studies have been reported in literature. While in many cases, the properties of the multilayer structure behave in the predicted manner, in others new effects are produced which lead to unexpected behaviour. The origin of these new effects in most cases is poorly understood and is usually attributed to some “interface effects” or generation of stresses due to different components of the multilayers. In many cases, the properties of the multilayer structures are found to depend strongly on the thicknesses of the constituent layers. Moreover, the properties are found to change dramatically when the sub layer thicknesses are reduced to low values. This indicates that in the multilayer structures, there is some characteristic length scale which controls the properties. This characteristic length scale may arise because of phenomena such as diffusion or generation of stresses.

Barium strontium titanate (Ba_xSr_1-xTiO₃, BST) thin films are of interest for several applications such as cell capacitors in dynamic random access memories (DRAM), tunable microwave devices, thermal imaging arrays, optoelectronic devices,  humidity sensors, etc. A number of multilayer structures with BST as the major constituent such as BST/PZT/BST, BST/PLZT, BST/MgO/BST etc. have so far been investigated and enhancements in properties have been reported.

In this presentation, the available literature on the multilayer electroceramic thin films will be reviewed. Some results obtained by us    using the BST- ZrO2 multi-ayer structures as a model system will be presented. The diffusivity of Zr is low in several oxides so that a relatively clean interface between BST and ZrO₂ is expected to be maintained. The leakage current is found to change significantly upon introduction of the zirconia layers; however, this change is not monotonous with the thickness or the number of zirconia layers. XPS studies are used to demonstrate clearly the existence of a characteristic length scale controlling the leakage current behaviour with variation in multilayer structures. The leakage current and dielectric behaviour of the multilayers is compared with homogeneous BST- ZrO₂ thin films.

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I-15A                                                                                            118

HIGH DENSITY PLASMA PROCESSING OF

GATE DIELECTRICS FOR TFT APPLICATIONS

 

P. C. Joshi

 

SHARP Laboratories of America, Inc., LCD Process Technology Lab.,

5700 NW Pacific Rim Blvd, Camas, WA 98607

 

The high-density PECVD technique is promising for the low temperature processing of gate dielectric films for thin film transistor (TFT) devices integrated on glass, plastic, or other low temperature substrates. The Si/SiO₂ interface quality and dielectric reliability become increasingly important for future high performance TFT devices requiring thinner gate dielectric. In this paper, we report on the low temperature processing of thin SiO₂ gate dielectric films by High-Density PECVD technique employing an ICP plasma source. The high plasma density and low plasma potential of the ICP plasma are attractive for controlling the bulk and interfacial characteristics of SiO₂ thin films. In comparison to a conventional PECVD process, a high-density PECVD technique offers potential advantages of the deposition of higher quality films at lower processing temperatures by independent control of ion flux and ion energy during deposition and lower process induced impurity levels.

The SiO₂ fabrication process was optimized by correlating the process variables and thin film properties. The optical, electrical, and reliability characteristics were investigated in the thickness range of 100-500Å. The electrical performance was evaluated in terms of the leakage current, breakdown field strength, flat-band voltage, and interface trap concentration. The MOS capacitor reliability was evaluated in terms of the flat-band voltage shift, measured from high frequency C-V characteristics, under bias-temperature stress conditions. The device feasibility of the HD-PECVD SiO₂ thin films was established in terms of the poly-Si TFT characteristics. The performance of poly-Si TFTs, employing 300 and 500 Å thick gate dielectric, was evaluated in terms of the transfer and gate leakage characteristics. The observed electrical and reliability properties of the MOS capacitors and TFTs show the potential of the high-density plasma process for the low temperature processing of gate dielectric films for advanced TFT devices.

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I-16A                                                                                            188

ANTI-PHASE BOUNDARIES AND THEIR MODIFICATIONS USING SWIFT HEAVY ION IRRADIATION IN EPITAXIAL MAGNETITE THIN FILMS

 

¹Ravi Kumar, ²M.Wasi Khan,²J.P.Srivastava, ³S.K.Arora,³R.G. S.Sofin

and ³I.V. Shvets

 

¹Nuclear Science Center, Aruna Asaf Ali Marg, New Delhi-110067, India

²Aligarh Muslim University, Aligarh, India

³SFI Nanoscience Laboratories, Physics Dept., Trinity College Dublin, Ireland

 

Anti-phase boundaries (APBs)in epitaxial thin films of magnetite on MgO substrates are the natural growth process. APBs are modifying the physical properties of magnetite films from their bulk properties. In the present paper we have studied the APBs in two manners; by varying the film thickness and their madifications by swift heavy ion irradiation. Structural, magnetic and transport and noise properties of epitaxial magnetite thin films having varying density of antiphase boundaries (APBs) were investigated as a function of temperature and frequency. The noise was found to scale inversely with the frequency (1/f) and showed quadratic dependence on the bias current confirming that the noise arises due to the conductance fluctuations. The temperature dependence of noise is similar for all the films (15, 40 and 70 nm) except 7o nm films which exhibit sharp increase in its magnitude across the Verwey transition temperature (T_v = 104K).The magnitude of noise was found to increases with the decrease in film thickness. The sharp increase of noise in the vicinity of Verwey transition temperature is associated with the structural transition from cubic-monoclinic phase. The temperature and thickness dependent conduction noise is explained by the strain induced APBs density variation. Further, we have insvestigated the modifications of APBs by irradiating the films with swift heavy ion irradiations and found that the APB density is varying with the ion fluence value. The results are expalined on the basis of SHI irradiation induced structural strain and disorder in magnetite thin films.

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O-13A                                                                                            33

STRUCTURAL AND MORPHOLOGICAL HARACTERIZATION OF AlN FILMS DEPOSITED ON Si AND SiO₂/Si SUBSTRATES

 

J. P. Kar, G. Bose and S. Tuli, S. P. Behera

 

Centre for Applied Research in Electronics, I.I.T Delhi, New Delhi, 110 016, India

 

Aluminum nitride (AlN), a piezoelectric material with a high acoustic velocity, has attracted much attention for its excellent material properties such as wide bandgap, low electrical and high thermal conductivity, hardness and good chemical stability. Recent developments indicate that AlN film is a novel dielectric material for many silicon microelectronic devices and can be integrated in the signal-processing chip. Hence systematic study of AlN film grown on silicon as well as silicon dioxide is essential. In this paper structural and morphological characterizations of AlN films deposited on silicon as well as thermally grown SiO₂/Si (1 μm) wafers by reactive magnetron sputtering, have been reported. From X-ray diffractograms, the peak corresponding to (002) orientation of AlN deposited on silicon was found to be more intense than AlN/SiO₂/Si samples. The FTIR analysis shows the characteristic absorption bands of Al-N at 682 cm^-1 for both the samples. Different surface textures were observed by SEM studies. AFM investigations revealed that RMS roughness for AlN/Si and AlN/SiO₂/Si samples were around 2.1 nm and 2.8 nm, respectively.

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O-14A                                                                                            94

DIELECTRIC PROPERTIES OF POLYMER-CAPPED NANO-CRYSTALLINE ZnS FILMS BY WET CHEMICAL ROUTE

 

R.Maity, R. Goswami and K.K.Chattopadhyay*

 

Dept. of Physics, Thin Film & Nano Science Lab, Jadavpur University, Kolkata-32

kkc@juphys.ernet.in

 

II-VI compound semiconductors such as CdS, ZnS etc. have tremendous technological importance. These are widely used in many applications such as electroluminescent devices, solar cells and other optoelectronic devices. Nanocrystalline ZnS, CdS, etc. are very important materials due to their novel properties that arise from quantum confinement effect. Many synthetic routes have been employed to synthesize semiconductor nanoparticles including soft chemical reaction, solid-state reaction, sol-gel process, spray-pyrolysis methods, sonochemical preparation, and microwave irradiation. The wet chemical synthesis method is a simple and inexpensive alternative to more complex chemical vapor deposition (CVD) and physical techniques. This process is well appropriate for large area coating on simple and complex size of substrates. 

Initially, polymer-capped ZnS powder was synthesized from the mixture of zinc acetate, sodium sulphide in dimethyl formamide (DMF) using polyvinyl pyrrolidone. To prepare its thin films, dried powder was taken in a beaker containing 2-methoxy ethanol and was ultrasonicated. Then thin films were deposited on ultrasonically cleaned glass substrates by normal dip-coating procedure. The XRD spectrum showed various diffraction peaks originating from (111), (200), (220) and (311) planes of cubic zincblende phase of crystalline ZnS respectively. TEM micrograph of the PVP-capped ZnS films shows an abundance of nearly spherical crystallites, which have a mean particle size of ~5 nm. The selected area electron diffraction (SAED) pattern of ZnS nanoparticles shows the spots instead of rings due to single crystalline in nature. Optical studies were performed by measuring the transmittance of the films deposited on glass substrates in the wavelength region 300 to 800 nm. The high frequency dielectric constant (e) of PVP-capped ZnS nanocomposite has been measured and the value lies in the range 50-90 which is much higher than that of only PVP having dielectric constant ~28. The e value at lower frequency is very high than that at higher frequency. The e sharply decreases at lower frequency range and attains a nearly constant value at higher frequencies. The large value of dielectric constant of nanocomposite (PVP- ZnS) is due to the fact that the nanoparticles of ZnS within PVP are disconnected from each other and under the application of voltage, this nanoparticles act as nanodipole. As the particle size is nanometer ordered, the number of particles per unit volume increases, hence dipole moment per unit volume increases, so dielectric constant increases. So capacitance is also higher at low side frequency than higher range of frequency.

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O-15A                                                                                           133

ELECTRICAL PROPERTIES OF SOL-GEL PROCESSED FERROELECTRIC THIN FILMS

 

H. Basantakumar  Sharma

 

Department of Physics, Manipur University, Imphal 795003

hbsharma1@rediffmail.com

 

Electrical properties of ferroelectric thin films prepared by sol gel processing technique have been reported in this paper. Thin films of Barium titanium thin films have been prepared from Barium-2-ethylhexanoate and titanium(IV) isopropoxide precursors. The dielectric constant (΢) and loss tangent (tand) of the films at 1KHz were respectively found to be 380 and 0.01. The film also shows a well saturated polarization-field (P-E) hysterisis, showing ferroelectric nature of the film. The capacitance-voltage and conductance-voltage characteristics also show butterfly loops, confirming ferroelectricity in the films. The effect of fatigue on the electrical properties of the films are discussed and analyzed in this paper.

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PB-10                                                                                                                     180

A MICROWAVE CHARACTERIZATION TECHNIQUE FOR

THIN FILM FERROELECTRICS

 

K.Sudheendran, G.Lakshmi Narayana Rao, K C James Raju^*,

M. Ghanashyam Krishna and  Anil. K  Bhatnagar

 

School of Physics, University of Hyderabad, Hyderabad –500046, India.

kcjrsp@uohyd.ernet.in

 

We present the design of a simple coplanar wave-guide based test fixture for the microwave characterization of thin film ferroelectrics coated on substrates. Two identical 50-ohm CPW transmission lines are designed and fabricated on 0.2mm thick RT Duroid substrates. These CPW Trasmission lines are fixed to a rigid brass housing and the coaxial connectors are in turn fixed on to this housing. The entire test geometry is fixed on a movable platform made of brass, which internally activates the ground lines of the CPW. The test samples used for the measurement were the parallel plate capacitors with BST thin films as the dielectric. The thin film capacitors were connected to the CPW test fixture through wire bonding. The scattering parameters of the test fixture loaded with the thin film capacitor were measured using an Agilent 8722ES vector network analyzer.  De embedding with standard short and open structures were carried out to eliminate the parasite errors of the test fixture. The dielectric constant and loss of the thin films are determined from the measured complex S₁₁ of the thin film capacitor. The values obtained are compared with the dielectric constant and loss obtained for the same capacitor at 100MHz, as well as the value obtained at 5GHz using the coplanar resonator technique. This test fixture is found to be effective for the determination of the dielectric constant and dielectric loss of high k dielectric thin films at microwave frequencies, and can be used with capacitor structures of different sizes.

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PB-11                                                                                                                     154 

PREPARATION AND OPTICAL PROPERTIES OF

RF SPUTTERED PLZT THIN FILMS

 

Ravindra Singh¹, T.C. Goel² and Sudhir Chandra^1*

 

¹Centre for Applied Research in Electronics, IIT Delhi, Hauz-Khas, N.D.110016

²BITS-Pilani Goa Campus, Zuari Nagar, Goa 403720

 schandra@care.iitd.ernet.in

 

PZT and modified PZT thin films are of great interest, mainly because of the possibility of using them in applications such as: nonvolatile memories, optical waveguide devices, IR detectors, piezoelectric devices, sensors and actuators, electro-optic devices and MEMS etc. Amongst the various methods, sol gel and sputtering are the most attractive techniques  for preparing these films. While the sol gel technique has the advantage that the composition of the film can be varied and optimized easily, the sputtering process is compatible with IC technology. Furthermore, sputtering process also yields more reproducible and stable film properties. These two techniques are thus complimentary in developing the films for a given application.

In our previous work, we had prepared four compositions, namely 8/60/40, 8/70/30, 10/70/30 and 12/70/30 of PLZT thin films by sol-gel technique. From these compositions, 8/60/40 exhibited good ferroelectric properties. In the present work, PLZT (8/60/40) thin films were deposited on bare silicon, Pt/Ti/SiO₂/Si and quartz substrates by RF sputtering. For this purpose, a three-inch diameter target of PLZT (8/60/40) was prepared by conventional solid state reaction route. Various deposition parameters such as RF power, inter-electrode spacing, substrate temperature, annealing temperature etc. have been optimized to get oriented PLZT thin films. Structural analyses have been carried out using XRD. Surface morphology of different films has been investigated using SEM. Elipsometric studies have been carried out to determine the refractive index of the films. Band gap of the films has been determined using FTIR analysis. Optical transmittance of the films has been carried out using UV-Visible analysis. Applications of PLZT films for MEMS are discussed.

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PB-12                                                                                                                     179

FEQUENCY DEPENDENT DIELECTRIC PROPERTIES OF BARIUM STRONTIUM TITANATE THIIN FILMS IN THE PARA AND FERRO- ELECTRIC STATES

 

Venkata Saravanan, K C James Raju*, M Ghanashyam Krishna,

and Anil K Bhatnagar

 

School of Physics, University of Hyderabad, Hyderabad-500046

kcjrsp@uohyd.ernet.in

 

Thin films of Barium Strontium Titanate (BST) with chemical formula (Ba_1-x, Sr_x) TiO3 (x £ 0.5) was deposited on platinum coated quartz substrates.  Platinum was coated using dc- magnetron sputtering and the BST films were deposited by the sol-gel acetate route and also by RF magnetron sputtering. The crystal structure was characterized by X-ray diffraction and film morphology by scanning electron and atomic force microscopy. Capacitance-Voltage (C-V) characteristics of the (Metal-Insulator-Metal) MIM configurations were measured as a function of frequency and temperature in Para and Ferro-electric phase using an Agilent 4294A impedance analyzer. The polarization – electric field (P-E) and current- voltage (I-V) characteristics were measured using Radiant Technologies Ferroelectric Test System.

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PB-13                                                                                                                     131   

SOL-GEL PROCESSED BARIUM STRONTIUM

TITANATE THIN FILMS

 

S. Bobby Singh, H. B. Sharma, H. N. K. Sarma and P. Sumitra

 

Department of Physics, Manipur University, Imphal 795003

hnksarma@rediffmail.com

 

Ferroelectric Barium Strontium Titanate [Ba_xSr_1-xTiO₃ or BST] thin films with different Ba/Sr ratios have been prepared by conventional sol gel processing technique. The starting materials are Barium 2-ethylhexanoate, strontium 2-ethylhexanoate and titanium(IV) isopropoxide. The precursors except [TiOCH(CH₃)₂]₄ were synthesized in the laboratory. Stock solution for thin films synthesis was prepared by dissolving appropriate amounts of the precursors in a common solvent.  Thin films on different substrates were prepared by spin coating the stock solution at 3500 rpm, followed by pyrolysis at 400°C for 1 min in air. The effect of composition on its electrical properties has been discussed.

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PB-14                                                                                                                     187

CURRENT VOLTAGE CHARACTERISTICS OF VARIOUS COMPOSITIONS OF SOL-GEL DEPOSITED BARIUM STRONTIUM TITANATE  (Ba_XSr_1-XTiO₃) THIN FILMS

 

Sharmistha Lahiry* and A.Mansingh

 

Department of Physics and Astrophysics, University of Delhi,Delhi-110007

*Sri Aurobindo College, Univ. Of Delhi, Malviya Nagar, Delhi-17

 

For the DRAM application leakage current density of the thin film is an important aspect. The room temperature leakage current density of various compositions of Barium strontium titanate (Ba_xSr_1-xTiO₃, BST) (x=0.0,0.1,...1.0) were investigated. BST films were deposited by sol-gel method. The I-V and I-t characteristics were measured for films in the thickness range 0.5-0.57mm for samples of different composition. The effect of thickness was studied for one composition x=0.4. The I-t characteristics for different voltages were consistent with non-exponential decay of the form Iµ t^-n, where n was found to be in the range -0.42 to -0.6, but there was no systematic variatioon with composition. The log I vs log E, was found to be almost independent of thickness. Since the grain size were almost independent of thickness, so it may be inferred that the current is controlled by grain boundaries, rather than electrode film interface which has greater influence on dielectric constant. Regardless of composition, the I-V characteristics of  sol-gel films showed  distributed-trap space charge limited conduction, due to the fact that the I-V characteristics were determined mainly by  microstructure of the films. The I-V characteristics, for different composition film were ohmic at low fields and non-linear at high fields. The voltage at which non-linearity behaviour starts depends on the compositions. BST solid solution has higher onset voltages (~3.3V) than end members (1.5V for SrTiO₃ and 1.0V for BaTiO₃ films). This may be attributed to the scattering by different atoms in solid solution. This effect also reduces the leakage current of solid solution structures. The results are discussed in the light of different models for non-ohmic behaviour. The leakage current density was <1x10^-7 A/cm² at 1.5V, for films of different compositions  indicating the suitability for DRAM applications.  

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PB-15                                                                                                                     142   

EFFECT OF POLYMER VISCOSITY ON MORPHOLOGICAL, POLARIZING SWITCHING AND OPTICAL PROPERTIES OF POLYMER DISPERSED FERROELECTRIC LIQUID CRYSTAL THIN FILMS

 

Praveen Malik*, Pankaj Kumar*, K.K. Raina*# and Chander Prakash**

 

*Liquid Crystal Group, Materials Research Laboratory, School of Physics and Materials Science, Thapar Institute of Engg. and Technology, Patiala, 147004

** Electro Ceramics Group, Solid State Physics Laboratory, New Delhi 110 007

rainatietp@yahoo.com

 

Polymer dispersed ferroelectric liquid crystal (PDFLC) composite films are a novel class of optical materials used in flexible displays, holographic grating etc. These composite films usually comprised of low molecular mass liquid crystal (ferroelectric/nematic) dispersed (as micrometer sized LC-droplets) in optically transparent UV curable polymer.

In the present study, PDFLC films are prepared using ferroelectric liquid crystal (ZLI-3654) mixture and different viscosity UV curable polymers (NoA-73, NoA- 65, NoA- 63) by a standard polymerization induced phase separation (PIPS) technique. These PDFLC films were sandwitched between two Indium Tin Oxide (ITO) coated glass substrates separated by a mylar spacer of thickness 10µm. In this paper an effort have been made to study the effect of different polymer viscosity on the LC droplet morphology, polarizing switching and their optical properties. The average LC droplet size was measured in the range of 5- 55µm. Our result indicates that LC droplet size increases with increasing the polymer viscosity. The measured value of spontaneous polarization was found 7-9 nC/cm² and decreases with increasing the temperature. It is inferred that low viscosity PDFLC materials shows higher spontaneous polarization.

Acknowledgement: Authors gratefully acknowledge financial support by CSIR & DRDO

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PB-16                                                                                                                     169

ELECTRICAL MEASUREMENTS IN POTASSIUM NITRATE: POLYVINYLIDINE FLUORIDE COMPOSITE FILMS

 

Neeraj Kumar and R.Nath

 

Ferroelectric Materials & Devices Research Lab, Dept.of Physics, I.I.T. Roorkee

nrjphdph@iitr.ernet.in

 

The electrical conductivity and dielectric behaviour of Potassium Nitrate (KNO₃): Polyvinylidine Fluoride (PVDF) composite films have been studied. The conductivity variation with temperature during heating and cooling modes has been found to provide the knowledge of phase transition in the composite. In the composite the value of activation energies are lower as compare to pure KNO_3. The behaviour of dielectric constant has been measured during heating and cooling cycles at 100 kHz the value of dielectric constant is strongly dependent upon the phase transition from II-III phases on cooling. The dielectric loss has also been found to show phase transition in the composite. The Differential Scanning Calorimetry (DSC) experiment results also support the phase transition observed in the conductivity and dielectric measurements.

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PB-17                                                                                                                     122

Structural and Optical Properties of

PLZT (7/65/35) Thin Films

 

S.K. Pandey, S.N. Chatterjee, Anshu Goyal and Chandra Prakash

Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi-110054

 

T.C. Goel

BITS Pilani, Goa Campus, Goa-403726

 

Ratnamala Chatterjee

Department of Physics, Indian Institute of Technology, New Delhi-110016

 

PLZT materials have got their application in photosensitive phenomena that are directly linked to their microstructural, chemical, electronic, and optical properties, including (i) photoconductivity, (ii) photovoltaic properties, (iii) photo-assisted domain switching, (iv) ion-implantation enhanced photosensitivity, (v) photochromic effects, (vi) photomechanical (photostrictive) behavior, (vii) photorefractive effects, and (viii) photoexcited space charge phenomena. Unlike the PZT ceramics and other ferroelectric materials that are opaque, the most outstanding feature of the PLZT materials is their high optical translucency and transparency. Optical transparency is both a function of the concentration of lanthanum and the Zr/Ti ratio with a maximum in transparency occurring along the FE–PE (Ferroelectric-Paraelectric) phase boundary and beyond, until mixed phases produce. The PZT with Zr/Ti ratio (65/35) compositions shows better transparencies with La substitution between 8 to 16 mole %.

Here we report the growth of lead lanthanum zirconate titanate (PLZT) thin films (with molar ratio of Zr:Ti::65/35) deposited by the sol-gel technique on Pt/TiO₂/SiO₂/Si <111> (Pt/Si) and indium tin oxide (ITO) coated corning glass substrates. A seed layer of PbTiO₃ (0.1 mm) was coated by sol-gel on the substrates before depositing PLZT. A metal/ferroelectric/metal (MFM) structure was used for electrical property measurements. Electrodes were formed by depositing gold electrodes on top of the film. XRD, AFM, P-E and transmission measurements were performed. XRD analysis showed a single phase PLZT formation on both the substrates. AFM micrographs depicts nanometric average surface roughness (Ra=9.2 nm). Films grown on Pt/Si showed a well defined ferroelectric hysteresis loop at room temperature but a little pinched with remnant polarization, P_r= 9.7 mC/cm² and coercive field, Ec = 53.5 kV/cm. An optical band gap of 3.67 eV, as determined from transmittance measurements, was observed for the films deposited on ITO coated glass.  The possible mechanisms are discussed.

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PB-18                                                                                                                     123      

Microwave Tunable Ba_0.7Sr_0.3Fe_0.01Ti_0.99O₄ thin films deposited by PLD technique

 

L. Radhapiyari, A.R. James*, O.P. Thakur and Chandra Prakash

 

Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi-110054

*Defence Metallurgical Research Laboratory, Hyderabad

prakash@ssplnet.org

 

Ba_xSr_1-xTiO₃ is a promising material for application in tunable microwave devices as an applied field can vary its dielectric constant. Thin films of Ba_0.7Sr_0.3Fe_0.01Ti_0.99O₄ have been deposited on Pt-Si substrate by pulsed laser technique at different pressures and at a particular substrate temperature. PLD is a suitable technique for the deposition of  ferroelectric thin films because of (i) the stoichiometry of the films can be controlled as compared to other deposition techniques (ii) good crystallization of the films and (iii) the films can be deposited at high oxygen ambient pressure. The characteristics of the films are influenced by various parameters such as substrate material, substrate temperature, oxygen pressure and energy density during deposition.

XRD studies have confirmed the crystal structure of the films. The surface morphology of the films have been investigated by Atomic Force Microscopic studies and the films are found to be homogenous and crack free. The effect of oxygen pressure   on the dielectric properties such as dielectric constant (έ) and loss (tan δ) have been studied. The tenability of the films is determined from the variation of dielectric constant (έ) with applied field. The films deposited at lower oxygen pressure are found to have higher the dielectric constant and tunability while there is no significant change in the value of dielectric loss.  The observed variation in the dielectric properties is explained in terms of the oxygen vacancies generated during film growth.

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PB-19                                                                                                                       86

ELECTRON IRRADIATION EFFECTS ON

THE FERROELECTRIC PROPERTIES OF PMN-PT

RELAXOR FERROELECTRIC THIN FILMS

 

V M Jali^a, Aparna Shetty^a, Apurba Laha^b, Ganesh^c, S B Krupanidhi^b

 

^aDepartment of Physics, Gulbarga University, Gulbarga-585 106

^bMaterials Research Centre, Indian Institute of Science, Bangalore-560 012

^cMicrotron Centre, Mangalore University, Mangalore-574 199

 

The present paper deals with the study of the effects of electron irradiation on the dielectric and ferroelectric properties of 0.7 Pb (Mg_1/3Nb_2/3) O₃ - 0.3 PbTiO₃ [PMN-PT] relaxor ferroelectric thin film with a La_0.5Sr_0.5CoO₃ [LSCO] template layer. Solid solution of xPb(Mg_1/3Nb_2/3) O₃ – (1-x) PbTiO₃ [x = 1.0 – 0.65] is a well known relaxor ferroelectric material^1,2 possessing very high dielectric constant and has recently received gigantic attention for its potential application in thin film capacitors, mechanical actuators and transducers. The present group has made significant contributions in the field of the high-energy heavy ion irradiation effects on the dielectric, ferroelectric and electrical properties of ferroelectric thin films such as PZT, SBT, BST, and PLT ^3-5.

The films were grown by Pulsed Laser Ablation Deposition method on platinized silicon substrates in a Metal-Insulator-Metal configuration with circular gold dots as top electrodes. The temperature was varied from liquid nitrogen temperature to 220 °C to see the temperature dependence of dielectric constant, dielectric loss. C-V measurements were carried out in the temperature range R.T. to 220 °C and frequency range 1 kHz to 1 MHz.  The electron irradiation was carried out using Microtron accelerator facility. 8 MeV electrons with beam current 35 mA bombarded the films and the absorbed dose was 20 kGy. The films were well characterized prior to irradiation and then subjected to electron irradiation. Post irradiation characterization was carried out to see the role played by the electron irradiation on the material properties. The phase transition temperature, T_c remained same with an increased dielectric loss. The capacitance value decreased from its pre irradiation value.

Reference:

[1] G.A.Smolenskii,V.A.Isupov,A.I.Agranovskay,Sov.Phys.Solid State 2(1961) 2584

[2] L. E. Cross, Ferroelectrics 76 (1987) 241.

[3] Basavaraj Angadi, P.Victor, V.M.Jali, M.T.Lagare, Ravi Kumar and S.B.Krupanidhi,  

      Thin Solid Films 434/1-2 (2003) 40.

[4] Basavaraj Angadi, P.Victor, V.M.Jali, M.T.Lagare, Ravi Kumar and S.B.Krupanidhi,

      Materials Science & Engg. B 100/1 (2003) 93.

[5] Basavaraj Angadi, V. M. Jali, M. T. Lagare, V. V. Bhat, A. M. Umarji and Ravi

      Kumar, Radiation Measurements 36/1-6 (2003) 635.

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PB-20                                                                                                                        67

FILM THICKNESS DEPENDENCE PROPERTIES OF

BLT THIN FILM CAPACITORS

 

S. K. Singh^1,2 and H. Ishiwara¹

 

¹Interdisciplinary GSSE, Tokyo Inst.of Tech., 4259 Nagatsuda,Yokohama 226-8503, Japan

²School of Pure and Applied Physics, Guru Ghasidas University, Bilaspur-495009, INDIA

singh@neuro.pi.titech.ac.jp

 

Presently, the non-volatile ferroelectric random access memory (NvFeRAM) has become center of attention due to its lower power requirement and faster access speed.  Bismuth-layer- structured ferroelectric materials, such as SrBi₂Ta₂O₉ (SBT) and Ba_4-xLa_xTi₃O₁₂ (BLT), are the promising candidates for NvFeRAM due to their good fatigue properties and adequate remanent polarization. In order to achieve cost effective production of high density NvFeRAM above 256 Mb, the size of the cell must be below 0.6 μm². The reduction of feature size is accompanied by scaling of cell factor as well as operating voltage, access time and the read/write endurance. If cell size is below 0.6 μm², the operating voltage below 2V is essential and it demands a thinner capacitor. The thickness of the capacitor is restricted by the short circuit problem between the top and bottom electrodes. Here, we investigate the film thickness dependence properties of Bi_3.25La_0.75Ti₃O₁₂ (BLT) capacitor on silicon substrates. The BLT films were fabricated by a sol-gel method on Pt/Ti/SiO₂/Si <100> structures. The XRD data shows that all of the films had a polycrystalline perovskite phase, without any second phase. When film thickness is less then 50 nm, the layered perovskite structure exhibits week and broad peaks. The 50 nm thick film does not display polarization. Minimum thickness measured for polarization that could be limited to 80 nm of BLT films. Under the identical applied field, a remanent polarization (2P_r) in the BLT films was found to increase, whereas the coercive field (Ec) was found to decrease with the increase in film thickness. The leakage current density of the BLT films was in the order of 10^-7 A/cm² at 2V for 80 nm film. The surface morphology of the films was measured using atomic force microscopy. Initially, we observed plate-like grains, whose size was found to they reduce distinctively as the film thickness increased.

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PB-21                                                                                                                        60                                                                                                                                                                                                            

SOL-GEL PREPARATION OF RANDOMLY ORIENTED

Bi_3.25La_0.75Ti₃O₁₂ FERROELECTRIC THIN FILM

 

Rachna Sangha, Surya M. Gupta and Vinod K. Wadhawan

 

Ceramics Laboratory, Laser Materials Div., CAT,Indore 452013

 

There is considerable current interest in the application of BLT (bismuth lanthanum titanate) for ferroelectric random-access memories (FRAMs).  FRAMs are a class of memories in which data storage is nonvolatile like in ROMs (Read-Only Memories), but which provide fast read-write access like RAMs (Random-Access Memories). Randomly oriented BLT (Bi_3.25La_0.75Ti₃ O₁₂) thin films have been deposited by us using the sol-gel technique, which show a remanent polarization of 20 mC/cm² and a coercive field of 180 kV/cm when a 600 kV/cm field is applied. A number of layers (4 to 12) were spin-coated on a platinised-Si wafer using a sol prepared by nitrate-based bismuth and lanthanum precursors. An extra amount (20 wt.%) of bismuth nitrate (BLT20B) was found necessary to avoid the formation of the pyrochlore phase. The coercive field was found to be thickness-dependent and decreased with increasing thickness from 0.2 mm to 0.5 mm, which is explainable in terms of the blocking-layer model. X-ray analysis revealed the random orientation of the film. Field-induced polarization studies exhibited a nearly saturated loop for the BLT20B thin film. High remanent polarization (~ 20 mC/cm²) was found for the 0.4 mm thickness. High leakage current was observed in films of  thickness 0.2 mm, which decreased with increasing thickness.  The leakage current increases with initial increase of the applied field, and then tends to saturate at higher fields. The effect of applied electric field and frequency on the P-E hysteresis loop, and fatigue in the polarization switching for the film, will be reported. 

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PB-22                                                                                                                        04

Preparation and Characterization of pure

and manganese - doped layered Na₁.₉Li_0.1Ti₃O₇

 

Dharmendra Pal, Premchand*, Shripal

 

Physics Department, C.S.J.M. Univ.-P.P.N. College campus, Kanpur –208 001

*Physics Department, Indian Institute of Technology, Kanpur-208 016

 

Lithium (5%) mixed layered Na₂Ti₃O₇ and its 0.01, 0.02, 0.05, 0.10, 1.0 molar percentage MnO₂ doped derivatives have been prepared and characterized through d.c. conductivity in the temperature range 373-873K and room temperature EPR investigations. Three distinct regions have been identified in the log (σ_d.c T) versus 1000/T plots, the lowest temperature region is attributed to electronic hopping conduction (except for Na₁.₉Li₀.₁Ti₃O₇ (SLT) in which interlayer lithium ionic conduction being proposed) involving loose electrons of Ti₃O₇^2- groups, the room temperature EPR investigations reveal that at a lower percentage of doping the substitution of manganese ions occur as Mn³⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping, Mn²⁺ ions predominantly occupy both the two interlayer Na⁺ sites. The dilation of interlayer space has further been proposed  due to manganese ions  substitution at octahedral Ti⁴⁺ sites. In both  these cases the charged compensation mechanism should operate to maintain the overall charge neutrality of the lattice.

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PB-23                                                                                                                     159

STUDY OF ULTRATHIN LAYERS OF Ag₂S ON CORRODING Ag FILMS BY SURFACE PLASMON RESONANCE

 

Navina Mehan, Vinay Gupta, K. Sreenivas and Abhai mansingh

 

Department of Physics and Astrophysics,University of Delhi, Delhi-110007

                                                                                                     

The corrosion of a thin silver (Ag) film in air was studied by surface plasmon resonance (SPR) as indicated by the shifts in the position of the SPR resonance mode excited at the Ag-air interface. The Ag film (475Ǻ) was deposited by thermal evaporation on the hypotenuse face of a flint glass prism and exposed in air for a number of days. Energy dispersive analysis of X-rays (EDAX) studies confirmed the presence of sulfur in the corroded films, as expected. The experimental SPR reflectance curves were obtained using a He-Ne laser and laser power meter with detector. The SPR curve was found to become more and more broad and asymmetric with exposure time. The rate of growth of ultrathin layers of silver sulfide (Ag₂S) on the film surface (responsible for the corrosion of silver) was estimated over a period of 8 days by fitting the experimental data using Fresnel’s equations. This rate was found to be nearly linear with time with the formation of 40 Å of Ag₂S in 8 days. This was compared with similar data obtained by other workers by the ellipsometric technique, and was found to be in close agreement with it.

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PB-24                                                                                                                    151

PHOTOLUMINESCENCE CHARACTERISTICS OF

THIN FILMS OF SILICON NITRIDE

 

 Harish Bahadur*, D. Haranath*, Harish Chander*, A. Basu*, Rashmi*

Vivekanand Bhatt** and Sudhir Chandra**

*National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110012

** Centre for Applied Research in Electronics, I.I.T., Hauz Khas, N.Delhi-110016

 

Silicon nitride is a widely used material for photonics and MEMS applications. In MEMS, it is generally structural material.  In this work, we report our investigations on thin films of silicon nitride grown by RF sputtering technique and Plasma Enhanced Chemical Vapor (PECVD) Deposition on Si wafers.  Ellipsometric measurements using a manual research ellipsometer (Rudolph Research, USA) with an angle of 60B and the light of 546.1 nm showed that the refractive indices were in broad agreement with the reported values in literature. The film thickness for the PECVD grown sample was found to be 896 ± 32 nm and 1017 ± 29 nm for the RF Sputtered sample.

Photoluminescence measurements were conducted on a Perkin-Elmer LS-55 Luminescence spectrometer. Both types of the films were exposed to ultraviolet excitation. Both the films showed a distinct absorption peak centered around 200 nm. This contributed a very feeble and a broad emission   peak   at 445 nm. with a bandwidth of 150 nm. The PL for the intrinsic Si wafer also revealed a similar peak around 445 nm. Perhaps, the rf-sputtered film was not sufficiently thick and so was not effective in masking the emission due to intrinsic Si wafer. On the other hand, the PECVD grown film showed a well resolved triplet of PL peaks at 436, 478 and 526 nm. It must be mentioned that the absorption peak responsible for these emissions is again situated at 200 nm. The PL emission peak at 478 nm is attributed to silicon wafer with a slight apparent red shift. The other two peaks at 436 and 526 nm may have their origin in the impurity content present in the film. Further studies are in progress in identifying the cause for these emissions.

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SESSION VI B

PROCESSING & CHARACTERIZATION-II

Thursday, November 25, 2004

09.00 A.M.   -    11.00 A.M.

 

I-15B                                                                                            189

SINGLE CRYSTAL GROWTH OF HEXAGONAL FERRITES AND THEIR PERFECTION/DIELECTRIC CHARACTERISTICS

 

P.N.Kotru

 

Crystal Growth & Materials Research Group, Dept. of Physics & Electronics,

University of Jammu, Jammu – 180006.

 

Ferrites, in general, are technical materials which find applications as permanent magnets, magnetic recording, computer, microwave communication devices, radios and televisions, telecommunications and other applications such as in magnetostrictive vibrators, electromagnetic cores, copying machines etc. Hexaferrites, in particular, exhibit appreciable magnetic moment, high curie temperature and large anisotropy which make them useful for a number of applications. Devices operating at higher microwave and mm-wave frequencies are based on these materials. Consequently, these materials (mm-wave materials) are in great demand, which has generated renewed interest in hexagonal ferrites as “ classical high frequency ferrites”. These devices require high quality single crystals. Hexagonal ferrites are also the promising particulate media for perpendicular recording due to the chemical, morphological and magnetic characteristics. Substitution of suitable elements alters the characteristics of the magnetic materials and thorough investigations into the substituted hexaferrites will lead to tailoring of the magnetic materials as may be suitable for a particular device application. Swift heavy ion irradiation also affects the characteristics of hexaferrites as it may in other materials also. It, therefore, becomes important to understand the intrinsic characteristics of a material and their modifications on substitution and irradiation. For this study, it is advantageous to have material in the form of single crystals. The development of growth technology of perfect single crystals either in the form of bulk or as thin epitaxial films is of immense importance. The liquid phase epitaxial growth of hexaferrites has the requirement of a suitable substrate. The growth and defect characterization of Ga-In substituted and unsubstituted hexaferrites, employing surface techniques like microtopography, fragmentography, etching and bulk methods like X-ray topography are described and discussed with special focus on their utility as possible substrates for the liquid phase epitaxial growth of hexaferrite films. The dielectric behaviour of substituted crystals grown from flux, bearing chemical composition   SrGa_xIn_yFe_12-(x+y)O₁₉ (x=5, 7, 9; 0.8, 1.3, 1.0), is discussed. The modifications in their dielectric behaviour on irradiation with 50MeV Li³⁺ ions are dealt with. The dielectric behaviour in the temperature range of 30-500^oC and frequency range 1-10⁴ kHz is considered. The effect of frequency, temperature and composition on the dielectric constant (e^/), dielectric loss (tand) and a.c. conductivity (s_ac) helps in obtaining information about conduction phenomenon in ferrites based on localized electric charge carriers. The frequency variation of dielectric constant (e^/) and dielectric loss (tand) is explained on Koop’s phenomenological theory and hopping frequency of electrons between Fe²⁺ and Fe³⁺ on octahedral sites for both irradiated as well as unirradiated crystals.

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I-16B                                      

MEASUREMENT OF ELECTRICAL AND MAGNETIC PROPERTIES DURING MICROWAVE

PROCESSING OF CERAMICS

 

D. C . Dube

Department of Physics,Indian Institute of Technology, New Delhi – 110 016

 

Dinesh Agrawal

Materials Research Institute, Penn State Univ., University Park,USA

 

Microwave sintering is emerging as a technique to process advance materials. The process is time and energy saver, and often results in materials with better microstructure and better properties due to higher rate of reactions. Microwave processing has produced many new results such as de-crystallization of ferrites in the microwave field of the cavity in few seconds. In order to understand microwave-matter interaction better, It will be of interest if one can look for changes in the electrical and magnetic behavior of material during microwave processing. Keeping this in view, a experimental technique has been developed. The technique is based on combining a small measurement signal with the high power processing signal and permits studies either in electric or in magnetic field in a single mode cavity. Simple arrangement for coupling and decoupling of two signals is suggested. Some experimental results at 3.6 GHz up to 1200 C will be presented.

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O-01                                                                                              15

PBZT NANOCERAMICS SYNTHESIZED BY CO-PRECIPITATION AND SOL-GEL METHOD: A COMPARATIVE ANALYSIS

 

Puja Goel and K.L. Yadav

 

Smart Materials Research Laboratory, Dept. of Physics, I.I.T, Roorkee - 247667

klalyfph@iitr.ernet.in

 

Ferroelectric nanoceramics specifically lead zirconate titanate has been considered as a material of great technological importance in the development of high-density storage devices. The present day technology, which relies on the miniaturization of the structural components and need to use device structure in nanometer range in commercial product, requires fine-grained ceramics with uniform microstructures. The use of nanoceramics provides a change of both scientific and technological approach in the development of nanoscale devices. The microstructure and properties of these nanomaterials depend in an extreme manner on the synthesis method as well as on the processing route and it becomes important to select the most appropriate technique for preparation of these materials with desired properties. Therefore, there is a trend to develop such processing methods, which would provide PZT nano-powder with high chemical homogeneity and purity in a uniform microstructure, since these all are deciding factors in the production of ceramics for specified application. Many synthesizing technique exists with individual advantages and disadvantages depending on the requirements of the material. Commercially, PZT powders are produced using high temperature mixed oxide method, which eventually proved to be inadequate from the standpoint of chemical homogeneity, purity and uniformity. Presently two wet chemical processes i.e. Chemical coprecipitation and Sol-gel are employed to produce PZT nanopowdres. Chemical co-precipitation is a simple and inexpensive process, which makes it important for the industrial application whereas Sol-gel provides a control on the microstructure, morphology, size, size distribution, the agglomeration and the elemental distribution on the scale of nanoparticles but a bit more complicated and expansive for the commercial level production of powders. In this paper an attempt has been made to synthesize Bismuth doped PZT by sol-gel and co-precipitation method and compare the microstructure and crystallographic evolution of the compound. The crystallinity and the phase formation study have been completed by powder x-ray diffraction studies. The surface morphology, microstructure, grain size and distribution in the materials are being analyzed by using scanning electron microscopy. Details will be discussed at the time of presentation.

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O-02                                                                                               08

NEW MATERIALS FOR SPIN-ELECTRONICS

 

Aashish Bhardwaj and Vikas Kumar*

 

Guru Tegh Bahadur Institute of Technology, Rajouri Garden, New Delhi-110064

*Electronic Sc. Department, Kurukshetra Univ., Kurukshetra, Haryana -136119

aashish_bhardwaj@yahoo.com, vk_aggarwal@rediffmail.com

 

Spintronic devices exploiting the spin of electron rather than or in addition to charge are poised to revolutionize the electronics industry. Realization of this function, preferably at room temperature and above requires a focused materials effort. Also a complementary study of interface physics and chemistry at the mesoscale is needed, since the devices will mostly be thin film and heterostructure based. Magnetic semiconductors and  half metallic ferromagnets are the proposed future materials for spintronic devices. A study of the properties and applications of these materials and their comparison has been provided in this paper. Magnetic Semiconductors combine the ferromagnetic and semiconducting properties, also there are no interface problems or conductivity mismatch.

 

For magnetic semiconductors, study has been done for Mixed-Valence Manganese Perovskites A_1-XB_XMnO₃ (where A=La, Nd or Pr, and B=Ca, Ba, or Sr). These provide a  stronger magnetoresistance effect called Colossal Magnetoresistance (CMR) at the vicinity of Curie Temperature (Tc). Another choice for Magnetic Semiconductors are Europium Chalcogenides EuX (X=O, S, Se, Te) and diluted magnetic semiconductors (eg CdMnTe) which exhibit ferromagnetic phase below 2k. Half-metallic ferromagnets are another focus for spintronic materials, which have simultaneously both metallic and semiconducting characteristics and are 100% spin polarized. For these Heuslar alloys like Ni₂MnSb, half metallic oxides, transition metal pnitides (like MnAs, MnSb, CrAs, CrSb), diluted magnetic semiconductor oxide and Mn-doped ZnO have been discussed, which have great importance in the devices. Other half-metallic materials include Fe₃O₄ (magnetite) and CrO₂. These new materials may produce highly polarized sources that can be cast from solution onto complex surfaces. It is apparent that the development of new materials will continue to play a major role in the ongoing research on spintronics.

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O-03                                                                                               87

ELECTRICAL CONDNDUCTION AND MAGNETOELECTRIC EFFECT OF FERRITE – FERROELECTRIC COMPOSITES

 

M. B. Kothale* K. K. Patankar, and Y. B. Kolekar

 

Composite Materials Lab., Physics Department, Shivaji Univ., Kolhapur–416004

K. L. E. Society’s G. I. B. College, Nipani–591237, Karnataka

 

The magnteto – electric composite materials have immense importance in the field of fiber communication, microwaves, electronic industries, etc. The ferrite-ferroelectrics composites in the present case were prepared by standard ceramic method. The individual phases were prepared separately and pre-sintered at about 700⁰C Composites with composition xBa_0.8Pb_0.2TiO₃-(1-x) cu_0.6cu_0.4fe₂O₄ with x varying as 0.55, 0.7 and 0.85 were prepared by sintering at 800 C. The palletized samples were then finally sintered at 1050⁰C for 24 hrs. XRD analysis reveals the presence of both the phases in composites.

 

The variation of dc resistivity with temperature was studied. The dc resistivity decreases with increase in temperature suggesting semiconductor type behavior. The linear varoation shows a break at curie temperature. The activation energy was found to be 0.2eV. It suggests that the conduction is due to hopping of change carriers. To realize ME signal in composites the peletes were poled electrically by heating the samples 30⁰ C above the Curie temperature and cooled slowly. The magnetic poling was done at room temperature by applying do magnetic filed. The maximum value of ME output is found to be 135 mV/cm/Oe in case of the present composites. The ME effect increases with increase in ferroelectrics content of the composites. This is due to the increase in resistivaly and grain size. In general the lower value of ME output is attributed weak magnetoelectric interaction.

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O-13B                                                                                          145

SYNTHESIS AND ELECTRICAL STUDIES ON YTTRIUM COBLTITE SUBSTITUTED STRONTIM TITANATE

 

H.S. Tewari, Amit Godbole, O. Parkash* and D.Kumat*

 

School of Pure and Applied Physics, Guru Ghasidas University, Bilaspur (C. G.)

*Department of Ceramic Engineering, Banaras Hindu University, Varanasi (U. P.)

 

Most of the commercially used eletronic ceramics have compositions based on perovskite structure having general formula ABO₃ with A as a alkaline earth ion and B as a titanium or Zirconium or tin ion. The electronic properties of these materials are modifies by a variety of substitutions or suitably controlling the processing parameters.

Substitution in these materials is possible at A or B site independently or at both sites simultaneously. Strontium titanate doped with rare earth ions exhibit relaxor behaviour with increased permittivity. On heating in an atmosphere having very low pressure of oxygen, it becomes semi conducting and potentially useful as barrier layer capacitor material. Considering useful and interesting properties of this system, prompts us to prepare and explore the potential application of a similar series of compositions having general formula Sr_1-xY_xTi_1-xCo_xO₃ which represents the solid solution between strontium titante and yttrium cobaltite. In this paper, we are reporting the electrical conduction behaviour of this system. These studies important as electrical conduction plays an important role revealing the dielectric behaviour. Various compositions with x<0.10 in the system Sr_1-xY_x Ti_1-xCo_xO₃ prepared by high temperature solid-state reaction method. The formation of single-phase solid-solution was confirmed using powder x-ray diffraction. AC conductivity was measured on silver coated cylindrical pellets as a function of frequency at steady temperatures in the range 300 – 525 K using Hewlett Packard 4192A LF impedance analyzer. In the present study, two types of samples were studied. One set of samples was quenched from the sintering temperature (1623 K) prepared while the other set of samples with same compositions were annealed at 1273 K and then furnace cooled. From the detailed study on these materials, it is concluded that quenching produces strain in the lattice which gives rise to more equivalent hopping sites of almost equal and effective barrier energy for hopping is reduced. Hence, the conductivity of quenched samples is due to variable range hopping conduction and annealed sample activated hopping conduction.

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O-14B                                                                                          150

CHARACTERIZATION OF THIN FILMS OF ZnO

 

Harish Bahadur*, A.K. Srivastava*,, M. Kar*, Rashmi*, K.N. Sood*,

Ram Kishore*, A. Basu*, R.K. Sharma*, S.B. Samanta*,

Vivekanand Bhatt**, Prem Pal** and Sudhir Chandra**

 

*National Physical Laboratory, Krishnan Road, New Delhi-110012

** Centre for Applied Research in Electronics, I.I.T., Hauz Khas, N.Delhi-110016

 

Zinc oxide,   in its thin film form, continues to be a versatile material of significant interest in various technological applications such as piezoelectric transducers, transparent conductor and surface acoustic devices and a variety of sensors,  Consequently, thin films of ZnO are grown by a variety of methods such as vacuum evaporation, reactive evaporation, sputtering, MOCVD, sol-gel chemical solution deposition, chemical vapour deposition and spray pyrolysis etc. It is known that ZnO has a wurtzite structure having a number of alternating planes composed of fourfold coordinated O^2- and Zn²⁺ ions stacked alternatively along c-axis.  It can thus be considered as two interpenetrating hexagonal closed-packed lattices of Zn and O. The preparation of ZnO thin films has been the subject of continuous research for a long time because the properties of ZnO films depend upon the method of preparation. Because of its high piezoelectric coefficient, ZnO has a great potential for applications as vibration sensor. We aim at using thin films of ZnO for MEMS-based acoustic resonator. Characterization and preparation of thin films of piezoelectric materials thus forms an important part of our project of integrating such films into MEMS based acoustic sensing devices. An estimation of the characteristics of the films would not only be cost effective in selection o f the film for device fabrication but will also make the device reliable.

We present here a report of our characterization results of the thin films of ZnO grown by sol-gel process and RF sputtering. The techniques involve, Ellipsometry, XRD, Scanning and Transmission Electron Microscopy, Scanning Tunneling Microscopy, Optical Absorption, EDS. on films prepared show the formation of zinc oxide phase. Nano-structured fine grains of size ranging from 20-60 nm were observed with zinc nitrate precursor film. Individual grains show a sharp contrast with different facets and boundaries. Crystal planes and lattice parameters calculated by both electron diffraction and X-ray diffraction and estimated by STM are quite close and in agreement with the reported values in literature.

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O-15B                                                                                         156

FABRICATION OF A ZnO/LiNbO₃ SURFACE ACOUSTIC WAVE UV LIGHT DETECTOR

 

Sanjeev Kumar* and K. Sreenivas

 

Department of Physics and Astrophysics, University of Delhi, Delhi-110007

sanjeev@scientific.net

 

The interaction of surface acoustic waves (SAW) and optically generated charge carriers has led to the development of a new class of wireless ultraviolet light detectors.  Materials such as GaN and ZnO/LiNbO₃ bilayer structures have been tested, and SAW propagation in these materials is found sensitive to electrical changes generated by photo generated carriers on the surface.

In the present work, the response characteristics of a SAW device configured in the form of an oscillator using ZnO/LiNbO₃ bilayer structure for UV light detection has been investigated. Highly photoconducting ZnO thin films (71nm) were deposited on prefabricated LiNbO₃ SAW filter (center frequency 37 MHz) using a RF magnetron sputtering technique. The fabricated ZnO/LiNbO­₃ bilayer SAW device was connected to the positive feedback loop of a high frequency amplifier to design a SAW oscillator. The gain of the high frequency amplifier was controlled by V_cc, the power supply to the electronic circuitry. The ZnO/LiNbO­₃ SAW oscillator operating at 36.3 MHz was tested for incident UV light intensity in the range (0.4 to 34 mW/cm²). When UV light was illuminated on the ZnO/LiNbO₃ SAW oscillator, a shift in frequency and decay in the amplitude of the oscillator output were noted. The change in oscillator amplitude varied linearly with UV light intensity. A frequency downshift of ~ 28 KHz was observed when UV illumination (~34 mW/cm²) was chopped after 5 sec. The device exhibits interesting characteristics through the linear variation of shift in frequency and change in oscillator amplitude with UV intensity for UV light detection, or measurement applications, and can be effectively utilized for the development of a wireless detector.

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PB-25                                                                                                                       97    

SYNTHESIS STRUCTURE AND CHARACTERIZATION OF FERROELECTRIC Sr₅BiTi₃Nb₇O₃₀

 

Himanshu Sharma¹ and Kiran Kumari²

 

¹University Dept. of Physics, Veer Kunwar Singh University, Arrah 802301, Bihar

²Department of Physics, R N College Hajipur (Vaishali) 844 101, Bihar

drhimanshusharma@yahoo.co.in

 

Studies of phase transition and allied phenomena in tungsten bronze (T B) materials have received a great deal of attention from scientific as well as technological angles. As is already known that some niobates like BNN and potassium lanthanum niobate (PLN) continue to enjoy a special position on account of their enormous industrial uses. Even though the present compound Sr₅BiTi₃Nb₇O₃₀ (herein SBTN) has been suggested to be ferroelectric, no detailed study has been carried out either of its synthesis or of the establishment of its ferroelectric characteristics [1]. It was therefore considered worthwhile to synthesize and subsequently characterize the present material to have a better knowledge about it. The parent compound SrNb₂O₆ is known for its tungsten bronze (T B) structure. The crystal structure of T B compound consists of distorted NbO₆ ^–2 octahedra linked together at their corners in a complex way to three types of openings, which are occupied by A-site cations [2-3]. Out of the available six sites, only five are filled by the a-site (Sr²⁺) cations and one site, therefore, remains vacant. By the proper choice of heterovalent substitution for A and B cations, it is possible to fill the six sites by maintaining the overall charge neutrality. The resulting system therefore belongs to a charge compensated disordered tungsten-bronze structure of AB₂O₆type. The charge shortage due to the presence of tetravalent ions  (Ti⁴⁺) at B-site in the present case is compensated by the same amount of the excess charge resulting from the presence of trivalent ions (Bi³⁺) at the A-site. The polycrystalline powders of SBTN have been synthesized in single phase form by the solid state-sintering route. The analysis of the room temperature (300 K) X-ray diffraction (XRD) studies reveals that it possesses orthorhombic structure in the paraelectric phase with lattice parameters a = 30.676Å, b =7.102 Å and c = 6.911 Å. The detailed analysis of dielectric constant () and dielectric loss (tan d) as a function of frequency (.05KHz-10 KHz) at room temperature and also as a function of temperature  (from liquid nitrogen up to 160 ⁰C) indicate a dielectric anomaly and consequent structural phase transition from ferroelectric phase to paraelectric one at 15⁰C.  It is also shown that this anomaly is representative of a first order normal ferroelectric  (F E ) phase transition.

References

1. H Sharma and Kiran Kumari Indian J. Phys. 76A(3) 267 (2002)

2. M E Lines and AM Glass Principles and Applications of Ferroelectric and Related Materials (Oxford University Press), (1977)

3. B.Jaffe, W.R.Cook & H.Jaffe Piezoelectric Ceramics (London & New Work:Academic), (1971)

 

Acknowledgement

We sincerely thank Prof R.N.P.Chuddary(I.I.T.Kharagpur) & Dr Rajeev Ranjan  (S.M.S.T.IT,B.H.U.) for assisting us in experiment and for helpful discussion respectively

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 PB-26                                                                                                                    107

EFFECT OF YTTRIUM AND SAMARIUM DOPING

ON THE STRUCTURAL PROPERTIES OF

STRONTIUM STANATES COMPOSITION

 

P.K. Bajpai, Mukul Pastor and Kuldeep Ratre

 

School of Pure & Applied Physics, Guru Ghasidas Univ., Bilaspur-495009

bajpai_pk@yahoo.com

 

Barium and strontium stagnates are widely studied as suitable semiconductor sensor materials [1]. This class of compounds shows Para electric behavior if doped with yttrium and sintered in inert atmosphere at very low oxygen partial pressure. For sensor materials, loosly sintered particles or thin films give better response as it is increase the effective area and/or makes gas particle percolation into bulk easy. Recently, we have shown that inherent charge neutrality created by vacancies in yttrium doped stagnates make them important materials for sensor applications [2].

In the present paper, effect of Yttrium and Samarium doping on the strontium stanates compositions are presented. The materials are using conventional solid state reaction route and structurally characterized using XRD and SEM. XRD data show that both materials are in single phase and lattice parameter decreasing with the percentage of doped Y³⁺ & Sm³⁺ increasing. The average experimental density for Y³⁺ and Sm³⁺ are 86% & 68% that of the theoretical density and the samples are loosely sintered. The average grain size estimated from SEM varies in the range of 2mm-3mm.

[1]        S.M. Sze,VLSI Technology, NewYork, McGraw hill (1988).

[2]        S. Neirman and J.Burn, J. Material Sc. 19, 737 (1984)

[3]        P.K. Bajpai, K. Ratre, M. Pastor & T.P. Sinha, Bull. Mater. Sc. 26, 461 (2003)

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PB-27                                                                                                                      92   

STRUCTURE AND DIELECTRIC PROPERTIES OF A_0.5B_0.5TiO₃ (A:B= MONO : TRIVALENT ELEMENTS) CERAMICS

 

Subrat Kumar Barik and R.N.P. Choudhury

 

Department of Physics and Meterology,

I I T Kharagpur

 

Nowadays, ferroelectrics properties are found in many oxides of different structural families. Among them, perovskites structural families have a large number and variety of ferroelectric compounds, which have been found very useful for basic understanding of ferroelectric phase transition and also for industrial applications. Though a lot of compounds of the perovskite family have been examined for the purpose, the titled compounds haven’t been given much attention. In view of the above importance of the compounds, we have carried out the detailed studies of structural, microstructure, electrical and dielectric properties of the above compounds.

The polycrystalline samples of A_1/2B_1/2TiO₃ (A= Na, K, Li; B= Bi, Sb) were prepared using a high-temperature solid-state reaction technique. The formation of the compounds and preliminary structural information were obtained by an XRD technique. The above compounds were found in orthorhombic system (i.e. distorted perovskites). Microstructures of the compounds show the uniform distribution of grains and high-density samples. Detailed dielectric and electrical studies provided ferroelectric and paraelectric phase transition above room temperature. Impedance studies of the compounds are in progress that would be discussed in details.

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PB-28                                                                                                                       79         

CARRIER MOBILITY MEASUREMENT AT

MICROWAVE FREQUENCIES BY USING SQUARE

AND CIRCULAR BIMODAL CAVITIES

 

D.V.B.Murthy, V.Subramanian and V.R.K.Murthy

 

Microwave Laboratory, Dept. of Physics,

I.I.T. Madras, Chennai-600 036

manianvs@iitm.ac.in

 

This paper describes a non-contact technique viz. Microwave Hall effect, for measuring the mobility of the carriers in semiconductors at microwave frequency.  This technique uses a bimodal cavity where the microwave electric field interacts with the free carriers in the semiconductor sample under an external static magnetic field applied perpendicular to the microwave electric field.  The two orthogonal modes oscillating at the same frequency in the bimodal cavity facilitate the measurement of induced microwave electric field in the direction normal to the applied electric and magnetic fields.  This paper explains the design and analysis of the X-band square (TE₁₀₁) and circular (TE₁₁₁) bimodal cavities. The cavity is excited using the coaxial probe coupling methodology. Teflon sample holder is used to place the semiconductor sample at the electric maximum of the bimodal cavity. A canceling channel, consisting of directional couplers, variable attenuators and phase shifter, is used to cancel the transmitted power due to the non ideal mode coupling. To attain the mode degeneracy and orthogonality, a tuning procedure is adopted and is also explained in this paper. A change in the transmitted power (S₂₁) observed due to the application of the steady magnetic field is directly proportional to the mobility. The results obtained on n-type silicon samples are presented in this paper.  The paper also discusses the procedures to increase the sensitivity of the measurement. This technique is useful in measuring the mobility of the semiconductors and heterostructures.

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PB-29                                                                                                                      85

ENHANCEMENT IN DIELECTRIC PROPERTIES OF (Pb_0.8Ba_0.2)(Yb_0.5Ta_0.5)O₃ CERAMIC BY OXYGEN ANNEALING

 

Dibyaranjan Rout,V.Subramanian*, K.Hariharan,

V.Sivasubramanian⁺ and V.R.K.Murthy

 

Department of Physics, IIT - Madras, Chennai-600 036, India

⁺Materials Science Div., IGCAR, Kalpakkam 603102

manianvs@iitm.ac.in

 

The influence of oxygen annealing on the dielectric response of (Pb_0.8Ba_0.2)(Yb_0.5Ta_0.5)O₃ ceramic has been investigated. Conventional solid-state reaction method is followed to prepare the above system. The sintering condition is optimized at 1300 ^oC for 2 hrs.  To investigate the effect of oxygen annealing, the sample is annealed at 800 for 8 hrs in oxygen atmosphere. The   X-ray diffraction has been carried out to check the phase formation for both the as sintered and annealed sample. The density of the two samples is measured by Archimedes liquid displacement method. The dielectric measurement on these samples has been performed at 1 to 200 kHz in the temperature range –115 to 145 ^oC. A significant change in the dielectric response has been observed for the annealed sample. The dielectric constant increased and the dielectric loss tangent decreased for the annealed sample compared to as sintered sample. The temperature corresponding to the maximum value of dielectric constant slightly increased whereas the temperature corresponding to the peak value of dielectric loss tangent decreased noticeably. The dielectric peaks of the annealed samples are observed to be more diffused. The diffuseness coefficient, which is a measure of degree of diffuseness, is calculated by fitting the data in modified Curie-Weiss law and it is found to be large for the annealed sample than the as sintered sample. The ac electrical conductivity (s_ac) and activation energy are calculated.

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PB-30                                                                                                                      88

SYNTHESIS, CHARACTERIZATION

AND DIELECTRIC PROPERTIES OF

POLYANILINE-DYSPROSIUM OXIDE COMPOSITES

 

K.Sangshetty¹, Syed Khasim¹, M.Revanasiddappa²,

P.Narsimha¹ & M.V.N.Ambika Prasad¹

 

¹Department of Physics, Gulbarga University, Gulbarga – 585 106.

²Department of Chemistry, Gulbarga University, Gulbarga – 585 106.

Prasad1_Amb@rediffmail.com

 

In-Situ Polymerization of fine graded Dysprosium oxide (Nano Size) is carried out in polyaniline with different weight percent of Dysprosium oxide (10, 20, 30, 40 & 50 %) in polyaniline. The composites were characterized by using various techniques such as XRD, SEM, and IR spectroscopy. The molecular interaction of Dysprosium oxide with polyaniline is widely understood by these techniques.

Dielectric properties such as Dielectric constant and Dielectric loss were also measured using 4192 A Impedance Analyzer. It has been observed that in both the cases the values of Dielectric Constant and Dielectric loss decreases up to 30 wt % of Dysprosium oxide in polyaniline and increases there after. The observed behavior may be attributed due to percolation theory. The in-depth transport mechanism and possible applications of these composites are yet to be explored.

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PB-31                                                                                                                      64

DIELECTRIC CHARACTERISTIC IN THE GLASS CERAMIC SYSTEM [(Pb_1-xSr_x)O.TiO₂]-[2SiO₂.B₂O₃]-[7BaO]-[3K₂O]

WITH ADDITION OF La₂O₃

 

C.R. Gautam, D. Kumar, Om Parkash

Department of Ceramic Engg., Institute of Technology, B.H.U., Varanasi-221005

gautam_ceramic@yahoo.com

 

O. P. Thakur^§Chandra Prakash^§

§Electro Ceramic Division, Solid State Physics Laboratory, Delhi-110054

 

Glasses in the system [(Pb_1xSr_x)O.TiO₂]-[2SiO₂.B₂O₃]-[7BaO]-[3K₂O] (0.6≤x≤1.0) doped with 1 mol % La₂O₃  has been crystallized by suitable heat treatment on the basis of  differential thermal analysis (DTA). X-ray diffraction studies of these glass ceramics show that perovskite cubic lead strontium titanate solid solution crystallizes as a major phase. The addition of La₂O₃ enhance the crystallization of lead strontium titanate solid solution of perovskite phase in the glassy matrix and retards the formation of minor nonperovskite phases. Scanning electron micrographs show fine crystallites, uniformly dispersed in the glassy matrix. Results of the dielectric studies on glass ceramic system [(Pb_1-xSr_x)O.TiO₂]-[2SiO₂.B₂O₃]-[7BaO]-[3K₂O] show relaxor like behavior with very high value of dielectric constant. The value of dielectric constant for 1% La₂O₃ doped glass ceramic samples is very high in comparison to undoped glass ceramic samples. The high value of dielectric constant is attributed to space charge polarization at crystal glassy interface. The maximum value of dielectric constant and diffuseness of the peaks depend on the composition of the glass and the heat treatment schedule.

Keywords: Differential thermal analyses; Glass ceramics; Perovskite lead strontium titanate and Dielectric constant.

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PB-32                                                                                                                      65

ELECRICAL AND MAGNETIC INVESTIGATIONS

ON Sn SUBSTITUTED La_xBi_1-xFeO₃

 

Y.D.Kolekar^b, D.J. Salunkhe^a , S. B. Kulkarni^a and P. B. Joshi^a

 

^aDepartment of Physics Solapur University, Solapur –413 255.

^bDepartment of Physics, Shivaji university, Kolhapur – 416 004.

drpbjoshi@rediffmail.com

 

The composition La_xBi_1-xFeO₃ has been widely investigated owing to the occurrence of magnetoelectric effect in certain range of x. The material is observed to possess orthorhombic crystal structure for x= 0 and rhombohedral for x=1, with multiple morphotropic phase boundaries with varying x. The material is known to exhibit interesting anomalies in the vicinity of the morphotropic phase boundaries. For present studies we have selected x=0.2 in the vicinity of a morphotropic phase boundary. The literature review indicates that for x= 0.2, the Neal temperature is in the vicinity of  400 ⁰C, and an additional long range ordering at  ~ 60 ⁰C.    The electrical transition temperature Tc is reported to be below room temperature for excitation frequency at 1 MHZ. The investigations being reported are on the system Bi³⁺_0.2 La³⁺_0.8-x Sn⁴⁺_x Fe³⁺_0.8-x Fe²⁺_x O₃    for x= 0.0 to 0.4.

The system proposed above is peculiar in respect of:

1)      The Sn is being substituted at A site and it is a expectation that Bi and La  cations may maintain the perovskite crystal structure up to certain value of x and

2)      Because of substitution of Sn⁴⁺ the Fe ions may exist in oxidation state 2+ and 3+. This is similar to the La_1-xSr_x Mn³⁺_1-xMn⁴⁺_xO₃ or similar orthomanganites. As the system being investigated has A cations in the +4 and B cations in state 2+, we are reporting a entirely new ABO₃ system. The present paper reports preliminary observations on these compounds.

The system is investigated for crystal structure (XRD), Electrical permittivity Є_r   as a function T, in the frequency range 1KHz to 1MHz, electrical conductivity σ and magnetic susceptibility χ between 77K to 300K. The observations show that the substituted samples exhibit orthorhombic crystal structure with rhombohedral super lattice peaks corresponding to BiFeO₃. Observations of Є_r are characteristics of a relaxor material with Є_{r max} at 154900 for x =0.3 and temperature dependent Tc . The magnetic susceptibility studies reveal an additional long range ordering in the vicinity of room temperature. The T_N is observed at 385⁰C. The electrical conductivity is observed to indicate a semiconductor – semiconductor transition near room temperature. The detailed investigations on electric and magnetic characterization at low temperatures may reveal a valuable information about the material characteristics and ordering in 4+2+ ABO₃ systems.

 

Reference: -1) W.Kaczmarek et all physics letters vol. 47A, number 3(1974) 227-228

                     2) Z.V. Gabbasova physics letter A 158 (1991) 491-498                

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PB-33                                                                                                                      84

BAND GAP AND DEFECT MODE IN A DOUBLE PERIODIC ONE DIMENSIONAL MICROWAVE BAND GAP STRUCTURE

 

G. Santosh Babu^a, V. Subramanian^a, V.Sivasubramanian^b and V.R.K.Murthy^a

 

^aDepartment of Physics, IIT - Madras, Chennai - 600 036;

^bMaterials Science Division, IGCAR, Kalpakkam - 603 102.

manianvs@iitm.ac.in

 

Microwave band gap is a range of frequencies within which transmission of electromagnetic wave is attenuated. This paper reports microwave band gap in a double periodic one dimensional microwave band gap structure. The structure is constructed using glass (e_r' = 6.8, e_r^" = 0.1) and ebonite (e_r' = 4, e_r^" = 0.25) sheets. The transfer matrix method is used to calculate the band structure, density of modes and transmittance. The effect of creating a defect in this structure is also analysed using the above method. The transmittances are obtained over a frequency range of 10 to 20 GHz for this structure with and with out defect using a microwave vector network analyser and the results are compared with theoretically calculated values. The measured and calculated transmittances are in well agreement. It is also found that the width of the band gap of a finite size microwave band gap structure increases by creating the defect.

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PB-34                                                                                                                      56

STUDY OF (Sb, Cr) SUBSTITUTION AT  B  SITE IN

Pb_0.5Ba_0.5TiO₃ CERAMICS

 

S.A.Pawar, S.R.Kokare, N.T.Padal, S.B.Kulkarni and P.B.Joshi

 

Department of Physics, Solapur University, Solapur – 413 255.

drpbjoshi@rediffmail.com

 

The substitution of (Sb⁵⁺_x/2, Cr³⁺_x/2) for (Ti⁴⁺Zr⁴⁺)_x in PZT matrix has shown improvement in the dielectric and piezoelectric properties of the material. Here it is possible to stabilize the Sb ions in valance state 5+ for x < 0.15, though the starting material was Sb₂O₃. Another feature is the occurrence of piezoelectric anisotropy and improved pyroelectric properties for (PbCa) & (PbBa) TiO₃ compositions. Considering the requirements of the moderate curie temperature to realize a useful dielectric, piezoelectric, pyroelectric device the following systems are investigated for dielectric, pyroelectric and structural studies.

 

System-I         Pb_0.5Ba_0.5Sb⁵⁺_x/2Cr³⁺_x/2 Ti_(1-x)O              and

System II        Pb_0.5Ba_0.5Sb⁵⁺_x/2(Cr²⁺_x/4Ti⁴⁺_x/4)Ti⁴⁺_(1-x)O₃

where x is varied between 0.0 to 0.1

In case of system I the Cr is stabilized in state 3+, while in case of system II Cr is in state 2+. Sintering schedule was arranged properly to achieve the above shown valance compensation, using simultaneous investigations of the XRD. The compositions are studied using (i) X-ray diffraction and IR absorption studies, (ii) dielectric constant as a function of temperature (T) and frequency (f) both, and (iii) pyroelectric coefficient ф as a function of temperature. Observations on dielectric constant and complex impedance spectra suggest formation of grain boundaries possessing separate relaxation times. The composition shows improvement in the dielectric and pyroelectric properties at a certain level of substitution.

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PB-35                                                                                                                      09

CHARACTERIZATION OF NANOCRYSTALLINE CaTIO₃

PREPARED BY CHEMICAL ROUTE

 

M. Pal

 

Dept. of Physics, The Univ.of Burdwan, Golapbagh, Burdwan, W.Bengal 713 104

mrinalp@yahoo.com

 

Nanocrystalline CaTiO₃ have been synthesized by using soft chemical route.  X-ray diffraction study indicates that as-prepared powders were amorphous in nature and formation of CaTiO₃ phase start at about 773 K.  Phase formation saturates at around 1023 K.  Microstructure analysis by Reitvelt method revealed that the CaTiO₃ crystal size varies from 22.9 nm to 49.3 nm while the annealing temperature varies from 773 K to 1023 K.  The variation of dc resistivity with temperature (393 – 560 K) shows a polaronic behavior in this system.  Dielectric loss changes from 0.02 to 0.06 while frequency changes from 1 to 100 KHz.

Keywords:        Nanocrystalline, CaTiO₃, Chemical route, Reitvelt analysis, Dielectric loss.

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PB-36                                                                                                                      22

PREPARATION, CHARACTERIZATION AND PROPERTIES

OF 2SrO – 2CeO₂ – 5TiO₂ CERAMICS

 

G. Subodh and M. T. Sebastian

 

Ceramic Technology Division, Regional Research Lab., Trivandrum 695019

mailadils@yahoo.com

 

The recent exponential growth in wireless communication has made an increasing demand for dielectric resonators with stringent properties. The important characteristics required for a dielectric resonator are high dielectric constant for miniaturization,   high quality factor or low dielectric loss for better selectivity and low temperature coefficient of resonant frequency for stability. This limits the number of materials available for practical applications. Although there are several materials with dielectric constants in the range 10-75 with low loss, there are hardly any low loss materials with ε_r greater than 100. In the present paper we report the preparation characterization and properties of 2SrO – 2CeO₂ – 5TiO₂ ceramics. The samples are prepared by conventional solid state ceramic route.  The ceramics have high dielectric constant greater than 100. The effect of dopants on the microwave dielectric properties is discussed.

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PB-37                                                                                                                      10

SUBVALENT AND SUPERVALENT DOPING EFFECT

ON PZT CERAMICS

 

Ramesh Kumar Sharma and Raj Kumar Sharma

Department of Physics, DAV(PG) College, Dehradoon-248001

 

Puja Goel and K. L. Yadav

Smart Materials Research Lab., Dept. of Physics, I.I.T., Roorkee-247 667

 

Lead zirconate titanate (PZT) piezoceramic system, is a material of great technological importance, due to its increased application for transducers, capacitors and various microelectronic systems. Morphotropic phase boundary (MPB) composition (i.e. rhombohedral and tetragonal phase co-existed) of PZT system are known to have superior dielectric and piezoelectric properties. The properties of PZT can be enhanced in various ways, such as changing particle size, varying dopants concentration and composition, and by changing final sintered density. A lot of work has been done in the past to study the effects of substitution of single isovalent, supervalent or subvalent dopants with varying concentration in PZT for different device applications. But not much work has been done to report the effect of double doping at Pb site. In the present paper we report our work done on polycrystalline samples of Pb_1-x(La_zNa_1-z)_x(Zr_0.7T_0.3)O₃ (where, x= 0.1, z= 0, 0.01, 0.02, 0.03 (referred as PLNZT) prepared by solid state reaction method. X-ray diffraction studies of these samples suggest the formation of good quality and homogenous compounds. Detailed dielectric studies of the PLNZT compounds as a function of temperature in a low frequency region show that these compounds have diffuse phase transition with higher value of La concentration. Diffusitivity (g) study of phase transition provides its value between 1 and 2, indicating the variation of degree of disordering in the system. Studies on electrical conductivity provided some interesting physical parameters of the materials useful for devices.

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PB-38                                                                                                                      18

STUDY OF STRUCTURAL AND DIELECTRIC PROPERTIES OF Al DOPED PlZT CERAMICS

 

Radheshyam Rai^a, N.C. Soni^a, Seema Sharma*

and Prof. R. N. P. Choudhary**

 

^@Electronic Materials Division, National Physical Lab., N.Delhi 110012

*Dept. of Physics, BITS-PILANI_GOA Campus, Zuari Nagar-403726 Goa

**Dept. of Physics, Indian Institute of Technology, Kharagpur –721310

 

Ferroelectric of the perovskite family of general formula ABO₃ (A = mono or divalent, B = triad to penta valent ions) are very important because of their potential application such as dynamical and volatile memory component, Medical Ultrasound Applications, Gas Ignitors, Displacement transducers, Piezoelectric Transformers, Impact Printer Head sensors, Accelerometers and many other active and passive devices. PZT, a member of ABO₃ family is a solid-solution of ferroelectric lead titanate (PbTiO₃) and antiferroelectric (PbZrO₃) with varying degree of composition of the compounds [Pb(Zr_xTi_1-x)O₃ where 0<x<1]. The PZT ceramics with compositions near phase boundary offers good ferroelectric, piezoelectric and other properties. It is well established that the substitution of La³⁺ at the Pb site of PZT (abbreviated as PLZT) gives improved opto-electronic and piezoelectric properties of the materials, reduction of distortion in perovskite structure in PLZT and formation of high-density samples. In order to alter the properties of these PLZT ceramics to suit the needs of device fabricators, the effects of addition of various dopants with La were examined and the resulting effects were observed for certain Zr/Ti ratios. In this paper, we report the study of the effect of paired dopants in PZT ceramics i.e. Pb_0.9(La_x Al_1-x).1( Zr_0.65 Ti_0.35)_0.975 O₃ ( x =0.0, 0.3, 0.5 and 0.7) system.

Polycrystalline samples of double-doped PZT were synthesized by high- temperature solid- state reaction technique. Preliminary crystal structure and micro- structure of the compounds were studied using X-ray diffraction (XRD) techniques. Detailed dielectric studies of the samples suggest that they undergo second order ferroelectric-paraelectric diffuse phase transition. The change in the values of the dielectric constant and dissipation factor with Al concentration show very interesting behavior of the compound. Temperature dependence of d.c resistivity has also provided some interesting features of the compound.

References:

[1] T.Negas, G.Yeager, S.Bell, N.Coats, Am.Ceram.Soc.Bull 72(1993) 80

[2] H.Tamura, T.Konolle, Y.Sakable, k.Wakino, J.Am.Ceram.Soc 67(1989)C59

[3] K.Wakino, K.Minal, H.Tamura, J.Am. Ceram.Soc 67(1984) 278

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PB-39                                                                                                                      14

ESR, IR & OPTICAL ABSORPTION STUDIES OF Cu⁺² SPIN PROBE IN xLi₂O-(30-x)TiO₂-70TeO₂ 

TERNARY  GLASS SYSTEM

 

S.Suresh, J.Chinna Babu and V.Chandramouli*

 

           Department of physics, Osmania Univ., Hyderabad -500007, Andra pradesh

 

 ESR, IR and optical absorption spectra of xLi₂O-(30-x)TiO₂-70TeO₂ ternary glasses conataining Cu⁺² spin probe have been studied. From IR results it is clear that there exists TeO₄ (tbp) and TeO₃ (tp) units in the present glass system.  TeO₄ (tbp) units are converted into TeO₃ (tp) units with the addition of the Li₂O content.  Thus, Li₂O acts as a glass modifier while TiO₂ acts as a stabilizer and holds the TeO₄ units.  ESR results shows that the g_{|| >} g_^ indicating that the Cu⁺² ion is in tetragonal distorted octahedral site and ground state of the Cu⁺² is d_{x2- y2.}  It is observed that the g_||  and A_||  values gradually decreases with the increase of Li₂O  composition  and reaches a minimum at 15 mole % of Li₂O, however  beyond this composition  these values are increasing with addition of Li₂O content. These changes clearly indicate the structural change in the glass system.  Interestingly, the optical absorption peak of Cu⁺² is also found to be a maximum at x=15 % of Li₂O (or TiO₂ ) content.  Bonding parameters are calculated from the both Optical and ESR data found to change with the Li₂O concentration.

 

Key words. Spectroscopic studies, xLi₂O -(30-x)TiO₂-70TeO₂ glasses, characterization

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PB-40                                                                                                                      19

STUDY OF STRUCTURAL AND DIELECTRIC PROPERTIES OF Fe AND Nb DOPED PlZT CERAMICS

 

Radheshyam Rai^@ , Shikha Mishra^b, N.K.Singh^b and Seema Sharma*

 

^@Electronic Materials Division, National Physical Laboratory, New Delhi 110012

^bDepartment of Physics, V.K.S. University, Ara. 802301

*Dept. of Physics, BITS-PILANI_GOA Campus, Zuari Nagar- 403726 Goa

 

Ferroelectric of the perovskite family of general formula ABO₃ (A = mono or divalent, B = triad to penta valent ions) are very important because of their potential application such as dynamical and volatile memory component, Medical Ultrasound Applications, Gas Ignitors, Displacement transducers, Piezoelectric Transformers, Impact Printer Head sensors, Accelerometers and many other active and passive devices. PZT, a member of ABO₃ family is a solid-solution of ferroelectric lead titanate (PbTiO₃) and antiferroelectric (PbZrO₃) with varying degree of composition of the compounds [Pb(Zr_xTi_1-x)O₃ where 0<x<1]. The PZT ceramics with compositions near phase boundary offers good ferroelectric, piezoelectric and other properties. It is well established that the substitution of La³⁺ at the Pb site of PZT (abbreviated as PLZT) gives improved opto-electronic and piezoelectric properties of the materials, reduction of distortion in perovskite structure in PLZT and formation of high-density samples. In order to alter the properties of these PLZT ceramics to suit the needs of device fabricators, the effects of addition of various dopants with La were examined and the resulting effects were observed for certain Zr/Ti ratios. In this paper, we report, the effect of Fe, Mn, and Nb dopant with La on A site with different Zr and Ti ratio. Most of the work has been done on single dopants at A and B site. It has been observed that on substitution of single or double elements, there is a drastic change and modification in physical properties.

Polycrystalline samples of double-doped PLZT were synthesized by high- temperature solid- state reaction technique. Preliminary crystal structure and micro- structure of the compounds were studied using X-ray diffraction (XRD) techniques. Detailed dielectric studies of the samples suggest that they undergo second order ferroelectric-paraelectric diffuse phase transition. The change in the values of the dielectric constant and dissipation factor with Al concentration show very interesting behavior of the compound. Temperature dependence of d.c resistivity has also provided some interesting features of the compound.

References:

[1] T.Negas, G.Yeager, S.Bell, N.Coats, Am.Ceram.Soc.Bull 72(1993) 80

[2] H.Tamura, T.Konolle, Y.Sakable, k.Wakino, J.Am.Ceram.Soc 67(1989)C59

[3] K.Wakino, K.Minal, H.Tamura, J.Am. Ceram.Soc 67(1984) 278

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PB-41                                                                                                                      12

ELECTRICAL CONDUCTIVITY OF Al-SUBSTITUTED

BARIUM CERAMICS

 

K.G. Rewatkar*, N.M. Patil⁺, D.S. Bhowmick^#, P.M. Pokale^@

 

* Dept. of Physics, DMV College of Sc., Nawargaon, Dist. Chandrapur–442113

⁺ Dept. of Physics, LIT, Nagpur University, Nagpur.

^# Dept. of Physics, Radhikatai Pandav College of Eng., Umred Road, Nagpur.

^@ Dept. of Physics, Kavikalidas Institute of Technology, Ramtek.

vkrkishor@rediffmail.com

 

The conducting ceramics have been widely studied because of their technological significance as microwave device materials in low & high frequency range. The Al-Substituted Barium hexagonal oxides, with chemical composition BaFe₁₂O₁₉, were synthesized by standard ceramic technique and found to exhibit magnetoplumbite M-crystal symmetry. These oxides were characterized by X-Ray diffraction technique, from which lattice parameters were determined. On a polycrystalline material electrical and Seebeck coefficient measurements have also been carried out.

The a.c. conductivity of these compounds have been measured at various temperature and frequency. It follows the relation s(w)=Aw^S. The values of exponent (s) have been evaluated from the plot of log s(w) Vs log w. It was observed that the a.c. conductivity increases with frequency. The results were explained in the light of quantum mechanical tunneling (QMT) model satisfactorily for the present system.

Keywords:  Electrical conductivity, ceramics, X-ray diffraction, quantum tunneling etc.

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PB-42                                                                                                                      34

effect of tungsten doping on the Structural

and dielectric behavior of 

SrBi₂Ta₂O₉   FERROEctric ceramics

 

Indrani Coondoo , A. K. Jha^# and S. K. Agarwal^*

 

Dept. of Applied Physics, Delhi College of Engineering, Delhi-110042, India

^*National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi-110012, India

akj6467@indiatimes.com

 

In this paper, effect of tungsten doping on the structural and dielectric behavior of SrBi₂Ta₂O₉ ferroelectric ceramics is reported. Tungsten doped SrBi₂Ta₂O₉   ceramics, SrBi₂(Ta_1-xW_x)₂O₉ (0.0< x < 0.20) were synthesized by the solid  state reaction method. High purity powders of the constituent oxides in stoichiometric proportion were calcined in the temperature range of 900⁰C – 1050⁰C for 2 hours and sintered at 1230⁰C for 2 hours. The X-Ray diffractograms reveal that the single phase layered perovskite structure is formed when the doping content is x< 0.050 with no detectable secondary phase. Moreover, it has been found that the lattice constants of the layered perovskite decrease with increase in tungsten content except for the composition SrBiTa_1.95W_0.05O₉ , which show an increase in the lattice parameters. The dielectric measurements as a function of the temperature show that the Curie temperature decreases from 325⁰C (for x=0.0) to 295⁰C (for x=0.025) while over the composition range of x=0.050 to 0.20, the Curie temperature show an upward trend. Furthermore, the dielectric constant at their respective Curie temperature, increase with an increase in the content of tungsten. The dielectric loss reduces significantly on the introduction of tungsten.

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PB-43                                                                                                                      35

SYNTHESIS AND AC CONDUCTIVITY STUDIES OF

POLYPYRROLE – BaTiO₃ COMPOSITES

 

M.V.Murugendrappa¹, M Revanasiddappa², Syed Khasim³

and ^#M.V.N.Ambika Prasad³

 

¹Dept.of Physics, ²Dept.of Chemistry, GM Inst.of Tech., Davangere, Karnataka

³Department of Physics, Gulbarga University, Gulbarga, Karnataka

Prasad1_Amb@Rediffmail.com

 

Synthesis of Polypyrrole is carried out by chemical oxidation method by using ammonium per sulfate as an oxidant. BaTiO₃ is synthesized by oxalate route. Polypyrrole – BaTiO₃ composites were synthesized with varying weight percentage of BaTiO₃ by in-situ polymerization at 0 ⁰C. The ac conductivity of these composites were studied in the in the frequency range from 10² to 10⁶ Hz. It is observed that as the concentration of BaTiO₃ increases in the chain, the conductivity also increases and reached a maximum at 30 weight percent of BaTiO₃, where the ac conducting path is formed in the chain. However, as the weight percent of BaTiO₃ increases from 30 to 40, the conductivity decreases and beyond 40 weight percent it increases again. Hence polypyrrole – BaTiO₃ composites finds extensive technological applications.

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PB-44                                                                                                                      53

CHARACTERIZATION AND ELECTRICAL PROPERTIES OF POLYCRYSTALLINE Ca_0.1Sr_0.9La_xBi_1-xTa₂O₉

 

P.Sarah^a*, G.S.Kumar^b,  A.R.James^c, T. Radha Krishna^d and Rizwana^a

 

^aCVR College of Engg., Vastunagar, Mangalpalli, R R district-501 510, A.P

^bDept. of Physics, Material research lab., Osmania Univ., Hyderabad-500 007

^cDefence Metallurgical Research Lab., Kanchanbagh, Hyderabad-500 058, A.P

^dDept. of Physics, JNTU College of Engg., Kukatpally, Hyderabad-500 072

pasala_sarah@yahoo.com

 

SrBi₂Ta₂O₉ is given great attention due to the potential application in Ferroelectric random access memories. Substitutions in the perovskite-like slabs and in the (Bi₂O₂)^2- layers of SrBi₂Ta₂O₉ done to study the effects on the dielectric and conductivity properties. The mismatch caused by the substitution of ions in the lattice introduces significant distortion in the oxygen octahedral, improving the dielectric and ferroelectric properties enormously. In the present study Ceramic samples Ca_0.1Sr_0.9La_xBi_1-xTa₂O₉ with x = 0, 0.025, 0.1 are prepared by conventional solid state reaction sintering of high purity powder mixture of constituent oxides. The samples are finally sintered at 1200^oC. Samples are subjected to X-ray diffraction (XRD) to verify the formation of single phase. The morphological characterization is done by Scanning Electron Microscope (SEM). The distribution of grains is uniform and needle shaped grains are prominent. The compositional identification is done by Energy Dispersive Analysis by X-ray (EDAX). All the constituents are found to be present in the EDAX. Dielectric analysis includes measuring dielectric constant and loss as a function of temperature at different frequencies. There is a gradual decrease in the transition temperature and peak dielectric constant with lanthanum doping. The electrical properties are investigated by impedance spectroscopy as a function of frequency at different temperatures. The bulk a.c conductivity calculated from impedance data is plotted as a function of temperature and frequency.

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PB-45                                                                                                                      57

DIELECTRIC AND STRUCTURAL INVESTIGATIONS ON

(Sb, Fe) MODIFIED Pb_0.5Ba_0.5TiO₃ CERAMICS

 

S.A.Pawar, S.R.Kokare, N.T.Padal, S.B.Kulkarni and P.B.Joshi

 

Department of Physics, Solapur University, Solapur – 413 255.

drpbjoshi@rediffmail.com

 

Substitution of Ba at A site in PbTiO₃ offers a way of curie temperature engineering. Further, the (PbBa)TiO_3­ and (PbCa)TiO₃ compositions are observed to show piezoelectric anomaly, useful to device a low power ultrasonic phased array transducer. Additionally these compositions are observed to exhibit improved pyroelectric properties of the material in certain range of substitution. The present paper reports the investigations on the following systems:

System- I  Pb_0.5Ba_0.5Ti_1-xFe_x/2Sb_x/2O₃    and   System- II Pb_0.5Ba_0.5Ti_(1-0.75x)Fe_x/4Sb_x/2O₃

for x between 0.00 to 0.06 The systems mentioned above are selected considering the reports on modified PZT ceramics, where the substitution of (Fe³⁺_x/2, Sb⁵⁺_x/2) in place of Ti⁴⁺ shows improvement in the piezoelectric and dielectric properties of the PZT. Here in case of system I and system II Ti⁴⁺_x is replaced using (Sb⁵⁺_x/2, Fe³⁺_x/2) and {Sb⁵⁺_x/2 (Fe²⁺_x/4 Ti⁴⁺_x/4)} schemes of valency compensation respectively. The systems are investigated for the structural investigation (XRD), IR absorption studies, measurements of dielectric constant as a function of frequency and temperature both and pyroelectric properties. The observations of ε_r and complex impedance spectra have shown the effects similar to ABO₃ systems. Here multiple oxidation states of Fe are observed to show well separable grain and grain boundary contributions. The composition shows improvement in dielectric and pyroelectric properties at a certain level of substitution.

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SESSION VII

DIELECTRICS & RELAXATION MECHANISM

Thursday, November 25, 2004

11.15 A.M.   -    01.15 P.M.

 

 

I-17                                                                                                61

EFFECT OF ORDERING AND STRUCTURAL DISTORTION ON THE DIELECTRIC PROPERTIES OF Ba(Zn_1/3Ta_2/3)O₃

 

J Venkatesh and V.R.K.Murthy

 

Dept. of Physics, IIT, Madras, Chennai 600 036

vrkm@physics.iitm.ac.in

 

The effect of B-site ordering and structural distortion as a result of Sr substitution at the A-site of Ba(Zn_1/3Ta_2/3)O₃ (BZT) on dielectric properties were studied. The ordering was studied by TEM. The structural distortion was studied by both selective scan of X-ray diffraction peak present at the higher angle side of diffraction pattern and TEM. The quality factor strongly depends on the ordering and also structural distortion. The structural distortion has a major influence over sign and magnitude temperature coefficient of resonant frequency (t_f) of BZT.

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I-18                                                                                                41

COMPLEX IMPEDANCE ANALYSIS: A TOOL FOR

FERROELECTRIC MATERIALS

 

R. N. P. Choudhary

 

Department of Physics & Meteorology,

I. I. T.,  Kharagpur –721302

 

Complex impedance spectroscopy (CIS) has been shown to be an important and very convenient experimental tool to analyze the electrical and dielectric behaviour of ferroelectric ceamics. This technique enables us to correlate the changes in the physical properties of the materials with changes occurring in their microstructure/structure under varying conditions of temperature, frequency and concentration (of dopants if applicable). It has another advantage that it provides information about sample electrical parameters in terms of a unique relaxation frequency at a particular temperature that is independent of the sample geometrical factors. So the experimental results, on electrical and dielectric properties of a sample, obtained using this technique are inherently dependent on the intrinsic properties of the material and supposed to be basically unambiguous. Hence, the data can be used to model the sample properties in terms of an equivalent electrical circuit. 

In view of the above positive aspects of this technique, we have applied it to study electrical, dielectric, electromechanical properties etc. of a number of ferroelectric ceramics. The experimental results made it possible to visualize the physical structure of a polycrystalline sample as comprising of grains separated by grain boundaries. Further, the electrical processes occurring in the sample could be modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The real and imaginary parts of dielectric constants evaluated from impedance spectrum results have conveniently been expressed in terms of complex permittivity spectrum (Cole-Cole plot). The dielectric phenomenon in PLZT has been observed to be of polydispersive nature with marked deviation from Debye type relaxation process. This result has also been confirmed by complex modulus analysis.

The present talk aims to emphasize the applicability, suitability and unambiguity of complex impedance spectroscopy (CIS) technique in analyzing the electrical and dielectric properties of ferroelectric materials. The results of the investigations in our laboratory will be discussed as examples.  

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I-19                                                                                              102

THEORY OF ANTIFERROELECTRIC  PHASE TRANSITION

IN ADP TYPE CRYSTALS

 

T.C. Upadhyay* and B.S. Semwal

 

Physics Department, H.N.B.Garhwal Univ., Srinagar, Uttaranchal–246174

trilokphys@rediffmail.com

 

Ammonium dihydrogen phosphate (NH₄H₂PO₄), ammonium dihydrogen arsenate (NH₄H₂AsO₄), and their deuterated forms called ADP-type antiferroelectric have been intensively studied not only due to their potential applications in electro-optic optoelectrionic and display devices etc. but also due to their being model ntiferroelectric hydrogen bonded systems.  Very lattice theoretical work have been done on these antiferroelectrics as compared to ferroelectrics.  In this present study using four-sublattice  pseudospin-lattice coupled mode (FSPLCM) model alone with higher order phonon anharmonic interaction terms have been used.  The double-time temperature depended Green’s function method, has been applied to derive theoretically the expression for shift width, renormalized soft mode frequency transition temperature dielectric constant and dielectric loss.  By fitting model values of physical quantities from literature temperature dependences of shift, width, antiferroelectric soft mode frequency dielectric loss, for ADP crystal have been calculated across transition temperature, which compare well on the experimental data of Kaminow and Bush and Nagamiya.  Present study shows that soft mode theory successfully explains the dynamics of antiferroelectric transition in ADP in a quite simple way as the ferroelectric transition in KDP which shows the possibility of a unified theory.  The phonon anharmonic interactions play very important role at transition temperature and above it.

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O-16                                                                                               06

DIELECTRIC RELAXATION STUDIES OF TERNARY LIQUID MIXTURES OF ANILINE

AND SUBSITUTED ANILINES WITH ACETONITRILE

 IN THE MICROWAVE REGION

 

T.Kalaivani,  S.Kumar and  S.Krishnan*

 

Department of Physics, Annamalai University, Annamalainagar 608 002.

prof_krishnan@yahoo.com

 

Dielectric relaxation studies are helpful in studying the molecular structure and molecular forces in liquids and solutions in particular.  The nature and strength of molecular interactions have been established as the main cause for the chemical behaviour of compounds.  An attempt has been made to study the dielectric behaviour of three amines and their mixtures (i) N-methyl aniline +acetonitrile  (ii)Aniline+acetonitrile (iii)N,N-dimethyl aniline +acetonitrile at microwave frequency 9.36GHz at 303k.  Different dielectric quantities like dielectric constant(e^¢), dielectric loss(e^²), static dielectric constant (e₀) and dielectric constant at optical frequency(e_¥) have been determined.  The relaxation time (t) has been calculated by both Higasi’s method and Cole-Cole method.  The molar free energy of activation (DF_t) and (DF_h) have also been calculated.  The complex systems which were studied in this investigation shows the maximum relaxation  time  values at 1:1 complex ratio by both Higasi’s method and Cole-Cole  plot method.

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O-17                                                                                               90

DIELECTRIC-SPECTROSCOPIC AND A.C. CONDUCTIVITY INVESTIGATIONS ON LAYERED K_1.98Rb_­0.02Ti₄O₉

 

Shripal, L.N. Pandey, Deepam Maurya, R.P. Tandon* AND S.D. Pandey

 

Department of Physics, P.P.N. College Kanpur-208001

*Department of Physics and Astrophysics, University of Delhi, Delhi-110007.

 

The dependence of loss tangent (tand), real part of the dielectric constant (e’) and imaginary part of the dielectric constant (e’’) on temperature in the temperature range 373-773K and on frequency in the frequency range 20kHz-1MHz for 1.0% rubidium mixed K₂Ti₄O₉ ceramic sample have been reported.  The possible ferroelectric phase transition has been identified at 623K.  The 1n(s_a.c.T) versus 1000/T plots have been divided into four regions namely region I, II, III and IV.  The mechanism of conduction in temperature independent and highly frequency dependent region I may be attributed to the electronic hopping conduction along with exchangeable interlayer ionic conduction.  The less frequency dependent and temperature dependent region II may be attributed to the associated interlayer ionic conduction while more less frequency dependent and temperature dependent region III may be attributed to the unassociated interlayer ionic conduction.  The least frequency dependent and more temperature dependent region IV may be attributed to the modified interlayer ionic conduction.  Form log (s_a.c.) versus frequency curves, it can be seen that the slope decreases with the rise in temperature, suggesting that the electronic hopping conduction diminishes with the rise in temperature.

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O-18                                                                                             103

THEORY OF ELECTRIC FIELD INDUCED PHASE TRANSITION IN KDP-TYPE FERROELECTRIC CRYSTALS

 

T.C. Upadhyay*, Ramesh Singh and B.S. Semwal

Physics Department, H.N.B. Garhwal Univ., Srinagar, Uttaranchal–246174

trilokphys@rediffmail.com

 

Ferroelectric materials have got promising applications in modern technology such as memory devices, non-linear optical materials, piezoelectric, opto-electric, transducer, display devices etc.  Potassium dihydrogen  phosphate (KDP) crystals are important for laser fusion activity due to their ability to generate second and third harmonics of higher power Nd: YAG and Nd: glass lasers.  There have been great interest in the study of  dielectric, electrical and electrooptic properties of KDP-crystals recently.  In this paper we have studied the dielectric properties of KDP-type ferroelectric crystals.  Study of dielectric properties reveals about inter-and intra-moleculare interaction, confirmational changes in macromolectules as well as some possible applications of these materials in technology.  In KDP-type crystals hydrogen ion moves in double well potential along O-H…O bond.  Protons are ordered below transition temperature while they are disordered above transition temperature Cochran proposed that some of normal mode of vib ration of crystal becomes unstable (called soft mode) and as a result a transition from polar to non-polar (one crystal symmetry to the other) takes place.  This soft mode largely determines the dielectric properties of ferroelectrics.  Bline and  Zeks Ramakrishan and Tanaka, Quin et al, and Jhang et al have studied KDP-type ferrelectrics  using pseudospin model Ganguli used pseudospin-lattice coupled model (PLCM) along with a fourth order phonon anharmonic term.  We have considered third and fourth-order phonon anharmonic ingeraction terms in the PLCM model as well as external electric field term and applying double time thermal Green’s function method, obtained expressions for shift and width of  response function, soft mode frequency, Curie temperature  and dielectric  constant for KDP-type crystalline ferroelectrics.  By fitting model values of physical quantities from literature temperature dependences of soft mode frequency, and dielectric constant across transition temperature have been calculated which compare well with experiment of Baumgartner and also with experiment of Choi and Lockwood.  We find that though pseudospin part explains essential features of transitions but phonon part renormalizes the soft mode frequency.  The phonon anharmonic terms explain the temperature dependences of soft mode and dielectric properties both below and above Tc. These terms are very important, in explaining temperature dependences of dielectric and all other properties of KDP-type ferroelectric materials.

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PC-01                                                                                                                   100

THEORY OF ANTIFERROELECTRIC PHASE TRANSITION IN SQUARIC ACID TYPE CRYSTALS

 

T.C. Upadhyay* , Dinesh Chandra Bhatt and B.S. Semwal

Physics Department, H.N.B. Garhwal University, Srinagar, Uttaranchal – 246174

trilokphys@rediffmail.com

 

Antiferroelectric squaric acid (C4O4H2) crystal has a layered structure.  Each molecule is a square with oxygen ions at its four vertices linked by hydrogen bonds on equal footing.  At room temperature the layers are ferroelectrically  ordered and antiferroelectycally stacked. At about 371 K the crystal undergoes a first order phase transition to paraelectric phase.  A model of pseudospin type for layer 1 and 2 for squaric acid as has been considered by Lin and Qin is modified to includes pseudospin phonon interaction and cubic and quartic phonon anharmonic interactions.  With the help of the modified Hamiltonian and employing a double time thermal Green’s function technique of quantum dynamic, the expressions for antiferroelectric soft mode frequency spectrum.  Electrical susceptibility dielectric constant, loss, transition temperature are obtained for squaric acid crystal and its deuterated isomorph. Numerical values of different parameters appearing in theoretical expressions are fitted form literature and temperature variations far obtained.  Theses are compared with experimental results of Muser, Maiter et. al. and Samara & Semmingsen.           It is observed from the calculation that higher order phonon anharmonic interaction greatly influence the temperature dependence of the dielectric properties in squaric acid crystal.

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PC-02                                                                                                                   101

THEORY OF PHASE TRANSITION IN QUASI

ONE DIMENSIONAL PBHPO₄ –TYPE MONETITES

 

T.C. Upadhyay*, Subodh Gairola and B.S. Semwal

Physics Department, H.N.B. Garhwal Univ., Srinagar, Uttaranchal–246174

trilokphys@rediffmail.com

 

Ferroelectric materials have got promising applications in modern technology such as memory devices, non-linear optical materials, piezoelectric, opto-electronic, transducer, display devices etc.  The lead hydrogen phosphate (or PbHPO₄) and its isolmorphs form very interesting group (callled monetites) or H-bonded ferroelectrics similar to the vastly studied KDP group.  In these crystals the direction of spontaneous polarization is almost parallel to the direction of  the H-bond O-H-O projecting on the (010) plane.  The PO4 groups are bound to one another by the O-H-O bound in the form of a one dimensional chain along the c axis but the PO₄ chains in these salts are not bound to tone another by the H bonds.  Thus the interchain coupling between the chains is weaker then the intrachain coupling within a chain.  Therefore in these crystals unlike KDP crystals we consider a two sublattice pseudospin lattice coupled mode model along with third and fourth order phonon anharmonic interaction terms to obtain the expressions for shift, width, soft mode frequency dielectric constant and loss.  The method of double time temperature dependent Green’s function has been used for the evaluation of the above expression.  Using model values of physical quantities thermal variations of soft mode frequency, dielectric constant and loss have been obtained and compared with experimental results of Ohno and Lockwood and those of Negran et al. It reveals that the two sublattice PLCM model along with phonon anharmonic terms explains well the temperature dependences of soft mode and dielectric properties near phase transition.

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PC-03                                                                                                                      70

FERROELECTRIC PHASE TRANSITION IN Li₂Ba₂Nd₂Ti₄W₂Nb₄O₃₀

 

K. Jawhar, R.N.P Choudhary

 

Department of Physics & Meteorology, I.I.T., Kharagpur- 721302

 

Since the discovery of ferroelectricity in BaTiO_3, a large number of oxides of different structural family, including Tungsten-Bronze, have been examined in search of new ferroelectric oxides for device applications. Among them, some oxides with a complex Tungsten-Bronze structure (particularly some niobates) have been found very useful for many devices such as electro-optic, elasto-optic, pyroelectric, acousto-optic, non-linear optics etc. In our laboratory, we have studied a large number of compounds of this family. Recently, we have examined the ferroelectric properties and phase transition in a new complex compound Li₂Ba₂Nd₂Ti₄W₂Nb₄O₃₀ (containing 1, 2, 3, 4, 5, 6 valent elements and compound may be called 123456 compound). The polycrystalline samples of the compound have been prepared using a high temperature solid-state reaction technique. The formation of compound and preliminary crystal structure (system, unit cell dimension etc) have been checked using an X-ray diffraction (XRD) technique. Detailed studies of dielectric constant, tangent loss and hysteresis loop have confirmed the ferroelectric-paraelectric (FE-PE) phase transition in the compound with transition temperature much above the room temperature (ie, 350°C). The nature of phase transition in the compound is very much similar to that of Pb₅Ge₃O₁₁. Studies of electrical conductivity (AC/DC) and complex impedance of the compound have provided many interesting experimental data for better understanding of the nature of phase transition, and the quality of the material for applications. The details of our studies will be presented and discussed in the seminar.

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PC-04                                                                                                                      76

DIELECTRIC RELAXATION STUDY OF  THF WITH CYCLOHEXYLAMINE AND DIETHYLAMINE

AT MICROWAVE FREQUENCY

 USING TIME DOMAIN TECHNIQUE

 

G.Parthipan, A.Kingson Solomon Jeevaraj^a, Prabhakar Undre^b,

P.W. Khirade^b, T.Thenappan^a and S.C.Mehrotra^c

 

^aDepartment of Physics, Alagappa University, Karaikudi-630 003

^bMicrowave Research Lab., Dept. of Physics,Dr.B.A.M Univ.,Aurangabad 431004

^cDept. of Electronics & Computer Science, Dr.B.A.M Univ., Aurangabad 431 004

phdparthipan@yahoo.co.uk

 

The dielectric relaxation study for THF-CYCLOHEXYLAMINE and THF-DIETHYLAMINE has been carried out over the frequency range of 10 MHz to 20 GHz at 35º C using the time domain reflectometry method over 16 concentrations. The bilinear calibration method on least square fit method has been used to obtain the static dielectric constant e₀ ,relaxation time τ and the dielectric constant at high frequency e_∞. The excess permittivity and excess relaxation time have been worked out, which provide information regarding the interaction among solutions. The dielectric parameters show systematic change with concentrations. The results are discussed in the light of the theory.

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PC-05                                                                                                                      83

DIELECTRIC CHARACTERIZATION OF LEAD BASED COMPOUNDS IN LOW AND HIGH FREQUENCY REGIONS

 

R. R. Vedantam^a, V. Subramanian^a, V. Sivasubramanian^b and

V. R. K. Murthy^a

 

^aMicrowave Laboratory, Department of Physics, I.I.T., Madras, Chennai – 600 036

^bMaterials Science Div., IGCAR, Kalpakkam 603102

 

The temperature variation of high frequency (130 MHz to 1 GHz) dielectric response of lead based compounds (Pb_1-xBa_x)(Zn_1/3Nb_2/3)O₃, (Pb_1-xSr_x)(Zn_1/3Nb_2/3)O₃ for x = 0.2 and 0.3, (Ba_xPb_1-x)(Yb_0.5Nb_0.5)O₃ for x = 0.15 and 0.2 is measured using coaxial probe technique. The variation in the dielectric response on substitution of divalent ions in the A-site is studied. The observed variation in the dielectric response is discussed in conjecture with the low frequency dielectric response.

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PC-06                                                                                                                      89

TEMPERATURE DEPENDENT DIELECTRIC RELAXATION STUDY OF N,N-DMETHYLFORMAMIDE IN N,N-DIMETHYLACETAMAMIDE AT MICROWAVE FREQUENCY USING TIME DOMAIN TECHNIQUE

 

Prabhakar Undre^a, S.B.Jagdale^b, S.N.Helambe^b, P.W.Khirade^a*

and S.C.Mehrotra^c

^aMicrowave Research Lab., Dept.of Physics, Dr.B.A.M.Univ., Aurangabad 431004

^b Microwave Research Laboratory, Deogiri College, Aurangabad.

^cDept.of Computer Sc. & Information Tech., Dr.B.A.M.Univ., Aurangabad 431004

prabhakar222@rediffmail.com

 

The dielectric relaxation study on N,N-Diemethylformamide [HCON(CH₃)₂] – N,N-Dimethylacetamamide [CH₃CON(CH₃)₂] binary mixture has been carried out at 13 concentrations over the frequency range at 10MHz to 20 GHz at 15, 25, 35, 45⁰C using Time Domain Reflectometry method. The bilinear calibration method and least square fit method have been used to obtain the static dielectric constant e₀, dielectric constant at high frequency e_¥, relaxation time t. By using these dielectric parameters the excess permittivity (e^E), excess inversion relaxation time (1/t)^E, Kirkwood correlation factor (g), Bruggeman factor were calculated. The investigation shows the systematic change in static dielectric constant and relaxation time of the system with change in the concentration and temperature. In the mixture both excess permittivity and excess inverse relaxation time is found to be negative. The negative (e^E) value indicates formation of multimer of dipole in the system where as the negative value of (1/t)^E indicates slower rotation of multimers. The ‘g’ and ‘a’ values indicate stronger intermolecular interaction between solute and solvent.

Key words :  Time domain reflectometry, Dielectric parameters, Excess parameters, Kirkwood correlation factor, Brugeeman factor.

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PC-07                                                                                                                      91

RESEARCH   ON   THE DIELECTRIC AND   ELECTRICAL CHARACTERISTIC OF (Ba_0.5R_0.5)₂O₇ (R=W, Mo) CERAMICS.

 

N.K. Singh and R.N.P. Choudhary*

 

Department of Physics, V.K.S. University, Ara – 802301

*Department of Physics & Meteorology, I.I.T. Kharagpur – 721302

 

Though ferroelectric, Piezoelectric  and Pyroelectric properties in the large number of organic, inorganic, polymer and semiconducting materials (Oxides and H-bonded) of different structural families are known today,  some tungstates and molybdates of the pyrochlore structured compounds of the general formula A2B2O7 were found to be very useful for many device applications, such as switching elements, thermistors, thick film resistors and materials for screen printing,  they have been recognized only recently as potential candidates for temperature-stable, low-loss, high permittivity dielectric applications.  We have observed that some neodymiumbased pyrochlores have more interesting properties for their better understanding and applications.  Detailed literature survey on the above compounds suggests that not much studies have been done on the titled compounds.  Therefore, we have planned to carry out structural, dielectric, electrical and ferroelectric properties of the titled compounds.

Polycrystalline samples of the compounds were synthesized by a conventional solid-state reaction method.  X-ray diffraction (XRD) studies confirmed the formation of single-phase compounds in the orthorhombic crystal system.  Particle size of the samples has been calculated using Scherr’s equation.  Extensive  studies of microstructure of the samples by SEM confirm homogeneity of the compounds.  Measurement of dielectric constant (Î) and loss tangent (tand) were carried out with a HIOKI 3532 LCR Hi-tester both as a function of frequency  (100Hz – 10kHz) and temperature (RT to 350^oC) at different frequencies (i.e. 1, 10 and 100 kHz) of the compounds.  As we did not get the dielectric anomaly above room temperature we are now carrying out measurement at low temperature dielectric properties of the compounds.  Electric (a c / d c) conductivity of these compounds was also measured in a wide temperature range, provide some interesting results.  Details of the work will be discussed in seminar.

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PC-08                                                                                                                      96

STUDY OF SOLUTE-SOLVENT INTERACTION

THROUGH DIELECTRICS BEHAVIOR OF

N, N-DIMETHYL ACETAMIDE IN ETHANOL

  

K.N.Shivalkar^a, Prabhakar Undre^a, G.M.Dharne^b, P.W.Khirade^a*& S.C.Mehrotra^c

 

^aMicrowave Research Lab.,Dept.of Physics,Dr.B.A.M.Univ., Aurangabad 431004

^b S .B .E. S. college of science, Aurangabad

^c Dept. of Computer Sc. & Info.Tech., Dr.B.A.M.Univ., Aurangabad-431004

kn_shivalkar@yahoo.com

 

Dielectric Behavior of N,N-Dimethyl Acetamide [CH₃CON(CH₃)₂] – Ethanol    [C₂H₅OH] binary mixture at different temperatures 15, 25, 35 and 45⁰C have been determined over frequency range of 10 MHz to 20 GHz. Using the Time Domain Reflectometry Technique in reflection mode for 11 different concentrations of given binary system has been used to measure reflection coefficient. Further Fourier transform and least square fit method have been used to obtain dielectric parameters such as dielectric constant (e₀) and relaxation time (t). The dielectric constant decreased with an increase in temperature where as it increased with increase in concentration. Relaxation  time decreased with an increase in temperature and concentration. By using dielectric parameters excess permittivity (e^E), excess inverse relaxation time (1/t)^E and Kirkwood factor (g^eff) has been worked out.

 

Key words :  Time domain reflectometry, Dielectric parameters, Excess parameters, Kirkwood correlation factor, Brugeeman factor.

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PC-09                                                                                                                      98

DIELECTRIC RELAXATION STUDY OF ALLYL BROMIDE - METHANOL MIXTURE USING TIME DOMAIN REFLECTOMETRY

 

G.M.Dharne^a, Prabhakar Undre^b, K.N.Shivalkar^b,

P.W.Khirade^b*and S.C.Mehrotra^c

 

^b S.B.E.S. college of science, Aurangabad

^a Microwave Research Lab.,Dept. of Physics, Dr.B.A.M.Univ.,Aurangabad 431004

^cDept. of Computer Science & Info. Tech., Dr.B.A.M.Univ., Aurangabad 431004

 

A Time Domain Reflectometry system was developed to determine the frequency dependence of the Dielectric constant and loss factor. Time Domain Reflectometry in reflection mode has been used to measure reflection coefficient in frequency range of 10 MHz to 20GHz. Dielectric relaxation study of Allyl bromide has been carried out in methanol for 11different concentrations at 15, 25, 35 and 45⁰C temperatures. The dielectric parameters viz. static dielectric constant (e₀) and relaxation time (t) have been obtained by the least squares fit method. Investigation shows the systematic change in dielectric parameters of the system with change in concentration and temperature. By using dielectric parameters excess permittivity (e^E), excess inverse relaxation time (1/t)^E and Kirkwood correlation factor (g^eff) has been studied.  

          

Key words :  Time domain reflectometry, Dielectric parameters, Excess parameters, Kirkwood correlation factor, Bruggeman factor.

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PC-10                                                                                                                      62

Dielectric relaxation in  Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃

Relaxor ferroelectrics

 

J Venkatesh and V.R.K.Murthy

 

Dept. of physics, Indian Institute of Technology, Madras, Chennai 600 036

 

Lead magnesium niobate (PMN) is a typical relaxor ferroelectrics material for its characteristic frequency dependent diffused phase transition and a lack of macroscopic macroscopic polarization even the temperature is reduced far below the dielectric constant maximum temperature.  The origin of frequency dispersion is due to the presence of the thermally reorientable dipolar clusters present in the compounds.  It has been experimentally observed that the substitution of Ti at the B-site leads to the decrease of the relaxor characteristics.  At around 32% substitution of Ti, the composition undergoes first order ferroelectric phase transition and devoid of relaxor nature. In the work we will present the results of a relaxation model proposed by Lu and Calvarin (1995) to understand the dynamics of freezing of these dipoles in PMN with respect to Ti substitution.

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PC-11                                                                                                                      05

Dielectric relaxation spectroscopic studies

of a few surfactants using

Time Domain Reflectometry technique

 

T.Ganesh^a, D.Balamurugan, R.Sabesan and S.Krishnan*

 

^aDepartment of Physics, SASTRA, Tanjore – 613 402

Department of Physics, Annamalai University – 608 002

prof_krishnan@yahoo.com

 

Dielectric Relaxation Spectroscopy (DRS) is a useful technique to investigate the molecular motions of the functional groups with dipole moments.  The dispersion in the region up to 10 _­GHz is attributed to hydrophobic interactions among the non-polar alkyl chains and the electrostatic interactions of the polar (or) ionic head groups with themselves, counterions and the solvents.  We report here the Dielectric relaxation spectroscopy measurements made on 1. Anionic Sodium Dodecyl Sulphate(SDS) 2. Cationic Cetyl Trimethyl Ammonium Bromide (CTAB), Dodecyl Pyridinium Chloride (DPC) in aqueous solutions in the high concentration region i.e beyond their CMC. Time domain dielectric data was obtained in the reflection mode in the frequency range of 10 MHz to 20 GHz using HP 54750A sampling oscilloscope and HP 54754A TDR plug in module in order to obtain the information about the micelle structure.  The viscosity measurements were also carried out to correlate the dielectric data. The relaxation time (t) was determined using Cole-Cole method and the distribution parameter (a) is almost non-dependent quantity on the concentration of the surfactants.  We have determined the function “P” is called normalized dielectric modulus which is an index to characterize the deviation of the solution from pure water behaviour and is more useful parameter than the (e¢) and (e¢¢) of solutions.

The result shows that the static permittivity (e₀) increases for anionic SDS up to 400 mM and cationic CTAB, DPC up to 60 mM , 160 mM respectively and decreases progressively beyond the CMC.  The relaxation time increases with increase of surfactant concentration, it is for greater than the Debye rotational relaxation time of  the free water species.  The observed average relaxation time is due to “bound water” or “water of hydration”, as they unable to rotate at frequencies near 1-2 GHz in contrast to free water.  The distribution parameter shows that there is no new relaxation mechanism is envisaged.

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PC-12                                                                                                                      44         

FERROELECTRIC PHASE TRANSITION IN

Te-MODIFIED BARIUM STANNATES

 

Ashok Kumar¹, R. N. P. Choudhary^*2, and B. P. Singh¹

 

¹Department of physics, T. M. Bhagalpur University

²Department of Physics and Meteorology, I.I.T., Kharagpur-721302

 

Since the discovery of ferroelectricity in BaTiO₃, a large number of perovskites of a general formula ABO₃ (A = mono/divalent, B = tri-hexavalent cations) have been examined for their suitability in a variety of solid-state devices. It is now well established facts that a partial substitution of suitable cations at A/B site results in abundant diversity of the behavior of compounds that makes it suitable for wide varieties of applications such as boundary-layer capacitor, humidity sensor, photodetector, transducers, electrooptic modulator, memory devices, etc.

Barium stannate (BaSnO₃) is a member of peroveskite oxides and does not show any ferroelectric phase transition. Te modified barium stannates (BaSn_1-xTe_xO₃ where x= 0, 0.05, 0.10, 0.15) provides an interesting result and ferroelectric phase transition above room temperature. This is a marvelous and encouraging result in the field of ferroelectricity. We have prepared Te modified BaSnO₃ by a solid-state reaction technique. The calcinations and sintering temperature have been selected using thermal analysis (TG and DTA). The formation of compounds was confirmed by x-ray diffraction (XRD) analysis. A preliminary structure analysis indicates that it has cubical cell at room temperature. The microstructure of this pellet samples has been obtained with the help scanning electron microscope (SEM). As we increase concentration of Te, Curie temperature and dielectric anomalies increases. Ferroelectric properties have been confirmed with the help of appearance of hysteresis loop. Impedance analysis indicates the existence of both grain and bulk resistance near the Curie temperature (~225⁰C-275⁰C). Above 300⁰C, the resistance of this sample is due to bulk resistance, that value decreases with increasing temperature. The decrease in bulk resistance with increasing temperature shows a typically semiconducting behaviour of the material (i.e Negative temperature coefficient of resistance (NTCR)). The a.c / d.c values of conductivity is well within the semiconductung range at higher temperature. Detailed of our structure and ferroelectric properties will be discussed. 

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PC-13                                                                                                                      21

Complex Impedance spectroscopy analysis OF Na₂Pb₂La₂W₂Ti₄Nb₄O₃₀ FERROELECTRIC CERAMIC

 

Piyush R. Das, B. K. Samantaray and R N P Choudhary

 

Department of Physics and Meteorology, I. I. T. Kharagpur

 

Since the discovery of ferroelectricity and electro-optic properties in barium sodium niobates (BNN), a large number of niobate and tantalate compounds have been studied for some device applications. Some ferroelectric oxides, in crystal, thin film and ceramic form with tungsten bronze (TB) structure play a major role in fabricating some solid-state devices, such as computer memory and display, pyroelectric devices, piezoelectric devices, electro-optical devices etc. There is a large scope to develop useful materials from this family. In view of the importance of new materials for device applications, we have planned to study the effect structural, dielectric and electrical properties of Na₂Pb₂La₂W₂Ti₄Nb₄O₃₀ ceramics.

Polycrystalline sample of Na₂Pb₂La₂W₂Ti₄Nb₄O₃₀ compound was prepared by a high-temperature solid-state reaction technique. X-ray diffraction study of this compound provides the basic crystal data as well as the quality of the compounds. Measurements of dielectric constant (ε) and dielectric loss as a function of frequency (100 – 1000 kHz) and different temperature (300 – 700 K) show that the above compounds undergo ferroelectric-praraelectric phase transition of diffuse nature. The electrical property of the compound was studied using Complex Impedance Spectroscopic technique. Details of work will be discussed.

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PC-14                                                                                                                      38

Studies of Dielectric and Electrical properties of K₂Ba₂Nd₂Ti₄Nb₄W₂O₃₀ Ceramics

 

Dillip K.Pradhan, B.K.Samantaray, R.N.P.Choudhary

and Awalendra K.Thakur

 

Department of Physics and Meteorology, I. I. T. Kharagpur-721302, India

 

Ferroelectrics materials, especially polycrystalline ferroelectric ceramics, are very promising for a variety of applications such as high permittivity capacitors, ferroelectrics memories, pyroelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermisters etc. Driven by materials utility, interest in this important area of R & D have grown considerably leading to studies on a large number of ferroelectric ceramics of different structural family such as perovskite, tungsten bronze, spinel etc. Some ferroelectric ceramic oxides with tungsten bronze (TB) structure play major role in fabricating solid-state ferroelectric devices due to their interesting properties. In view of an ever-increasing importance of new materials for device applications, we have taken up the present studies on a new complex tungsten oxide based on a combination of rare earth and alkaline earth metals. A preliminary investigation of the structural, dielectric and electrical properties of the material has been planned to be discussed.

 

Polycrystalline samples of K₂Ba₂Nd₂Ti₄Nb₄W₂O₃₀ were prepared by a high-temperature solid-state reaction technique. The synthesis conditions have been optimized by thermogravimmetric analysis (TGA). The X-ray diffraction studies have been carried out in a wide range of Bragg’ angle 2θ (20⁰ ≤ 2θ ≤ 80⁰) with a scan rate of 2⁰ per minute to confirm the formation of the compound and investigate its crystal structure.  The electrical parameters have been measured   using a. c. impedance spectroscopy. Measurements of dielectrics constant (ε) and tangent loss (tan δ) as a function of frequency at different temperature have provided many interesting properties of the compounds. The details of our result will be discussed in the seminar.

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PC-15                                                                                                                      45

DIELECTRIC RELAXATION STUDIES OF

DIMETHYLSULFOXIDE, NITRILES MIXTURES USING FREQUEMCY AND TIME DOMAIN TECHNIQUES

 

K. Kasthuru, R. Naraendran, S. Mayilavelan and R. Balakrishnan

 

Dept of Physics, K.M.C.P.G.S Pondicherry

 

An attempt has been made to study the dielectric properties of dimethylsulphoxide, nitriles mixture by Frequency Domain and Time Domain Techniques at room temperature. Time Domain Reflectometry in reflection mode was used to measure reflection co-efficient in frequency range 10 MHz – 20 GHz. In Frequency Domain, X- band microwave bench was used to measure the dielectric permittivity. The measured values of permittivity and dielectric loss have been used to evaluate distribution parameter and relaxation time by applying the standard methods. The variation of relaxation time for mixtures as a function of concentration of its components indicates the existence of inter-association or formation of complexes. The electric dipole moment values of the binary mixtures of dimethylsulphoxide, nitriles in benzene are greater than their individual components in benzene. The appreciable amount of polarization in these mixtures may arise due to the addition of several polar groups.

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PC-16                                                                                                                    181

MICROWAVE DIELECTRIC PROPERTIES OF (Zr₀.₈,Sn₀.₂)TiO₄

 

Pamu D, Lakshmi Narayana Rao G, James Raju K C*

 

School of Physics, University of Hyderabad, Hyderabad-500 046.

kcjrsp@uohyd.ernet.in

 

(Zr₀.₈,Sn₀.₂)TiO₄ (ZST) microwave ceramics have been prepared by the conventional solid-state method. ZnO and CuO were used as sintering aids. The phase purity, crystal structure, microstructure and the microwave dielectric properties of ZST have been examined by XRD, SEM, and Vector Network Analyzer. The crystallite size of the calcined powder lie in 30-60 nm range. The sintering aids and sintering procedure showed considerable influence on the densification of ZST. The density of the samples varied with the amount of additives and sintering procedure.  The Microwave dielectric properties such as dielectric constant (ε_r), quality factor (Q) and the temperature coefficient of the resonance frequency (τ_f) have been measured. The additives do not significantly affect the dielectric constants but they significantly influence the microstructure. The values of dielectric constants ranged between 35-40. However, the unloaded quality factors (Q x f) are strongly dependent on the type and the amount of the additives. The microwave dielectric properties were compared with the low frequency dielectric properties measured as a function of frequency and temperature. The sintering process and the way it influence the dielectric properties are discussed.

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PC-17                                                                                                                    143

DIELECTRIC CHARACTERISTICS OF GEL GROWN

YTTRIUM TARTRATE CRYSTALS

 

Sanjay Verma, Ravender Tickoo, K.K.Bamzai, P.N.Kotru

 

Crystal Growth and Materials Research Group, Dept. of Physics & Electronics,

University of Jammu, Jammu – 180 006 (India)

 

Results of dielectric characteristics of YT grown by gel method at room temperature are reported. The dependence of dielectric constant, dielectric loss and conductivity as a function of temperature and frequency of the applied ac field are analysed. Dielectric constant at room temperature decreases with increasing frequency and tends to attain saturation at higher frequency. The temperature at which the dielectric constant shows peak value is established as the transition temperature of the material under study. The dielectric constant shows peaks at 80 ⁰C and 210 ⁰C irrespective of the frequency of measurements. However, the peak value decreases with increase in measurement frequency. The degree of diffusiveness at transition temperature is calculated by

Where g is the degree of diffusiveness. The value of g at 1 kHz for transitions at 80 ⁰C and 210 ⁰C is 1.63 and 1.80 respectively suggesting that the values of g lies between 1 and 2 indicating diffuse transition. The conductivity is found to increase with increase in frequency at all temperatures (40 ⁰C – 250 ⁰C). Variation of conductivity with frequency is expressed by the relation s_ac = Aw^s where s = 0.82 for temperature 80 ⁰C. The dependence of tand with frequency and temperature is also analyzed. The results are presented and discussed.

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PC-18                                                                                                                      25

DIELECTRIC BEHAVIOUR OF PULVERIZED URDBEAN

AT MICROWAVE FREQUENCY

 

P.G.Gawali, B.S.Narwade, Rekha Pande and G.M.Kalamse

 

B.S.College, Basmath, N.E.S.Science College, Nanded– 431602, Maharashtra

 

Values of Dielectric Constant (΢), Dielectric Loss (΢¢), Relaxation Time (t) and Conductivity (s) of Pulverized Samples of Urdbean were measured for different packing densities at 9.84 GHz and at different temperatures (23°C to 53°C). Experimental results on powders of different relative packing fractions (d_r) have been used to obtain transformation to 100% solid bulk using correlation formulae of Landau-Lifshitz-Looyenga and Bottcher. The energy parameters for Dielectric Relaxation Process DF_t, DH_t & DS_t for Urdbean have also been calculated. There is good agreement between the calculated values of Dielectric Parameters and the values obtained experimentally for bulk. Results compared to the measured values showed that Landau-Lifshitz-Looyenga equation provided much better estimates than Bottcher Equation. This shows cohesion in the particles of Urdbean powder.

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PC-19                                                                                                                      26

DIELECTRIC BEHAVIOR OF BINARY MIXTURE OF

ISO-BUTYL ALCOHOL AND ETHYLENEDIAMINE

 

B.S.Narwade, P.G.Gawali, Rekha Pande, G.M.Kalamse

 

Degloor College, Degloor, Science College Nanded 431605 (M.S)

bhanu_narwade@yahoo.com

 

In the present paper we have obtained the values of dielectric constant (΢) and loss factor (΢¢) experimentally by using reflectomeric technique, for binary mixture of iso-butyl alcohol(IBA)and ethylenediamine (EDA) at 9.84 GHz microwave frequency  and 29⁰C temperature. The measured values of (΢) and (΢¢) have been used to evaluate the values of molar polarization (P₁₂).Also the excess values of permittivites(D΢,D΢¢), excess viscosity(Dh),excess square refractive index ( Dn_D² ) and excess activation energy ( DE_a) for viscous flow have been evaluated from measured dielectric data .We have used these parameters to explain the nature of complex formation in the mixture. The result suggest the strong interaction between molecules of amine and alcohol. 

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PC-20                                                                                                                      46

DIELECTRIC RELAXATION OF BUTOXY ETHANOL, THYL-1-HEXANOL & ISOPROPANOL IN FORMAMIDE AT MICRO-WAVE FREQUENCY USING TIME DOMAIN TECHNIQUE

 

U.Sankar^a, Prabhakar Undre^b, P.W. Khirade^b, T.Thenappan^c

and S.C.Mehrotra^d

 

^aA KGS Arts College, Srivaikuntam-628 619, Tamilnadu

^bMicrowave Research Lab.,Dept. of Physics, Dr.B.A.M Univ.,Aurangabad-431004

^cDepartment of Physics, Alagappa University, Karaikudi-630 003

^dDept. of Electronics and Computer Sc., Dr.B.A.M Univ., Aurangabad-431004

usankar2001@yahoo.com

The dielectric relaxation study for 2-butoxy ethanol-formamide,2-Ethyl 1-hexanol-formamide,Isopropanol-formamide has been carried out over the frequency range of 10 MHz to 20 GHz at 35º C using the time domain reflectometry method over 16 concentrations. The bilinear calibration method on least square fit method has been used to obtain the static dielectric constant e₀ ,relaxation time τ and the dielectric constant at high frequency e_∞. The excess permittivity and excess relaxation time have been worked out, which provide information regarding the interaction among solutions. The dielectric parameters show systematic change with concentrations. The results are discussed in the light of the theory.

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PC-21                                                                                                                      134

EFFECT OF TEMPERATURE ON THE DIELECTRIC BEHAVIOUR AND AC CONDUCTIVITY OF MAGNETO-FERROELECTRIC COMPOSITES Ba_0.8Pb_0.2TiO₃ + Ni_0.5Zn_0.5Fe_1.95O_4-δ IN THE FERROELECTRIC RICH REGION

 

K.Krishnaveni, N.Ramamanohar Reddy, M. Venkata Ramana, G. Rajitha,

E. Rajagopal, K.V.Sivakumar*, and V.R.K.Murthy¹

 

Ceramic Composite Materials Lab., Dept.of Physics,S.K.Univ., Anantapur 515003

¹Department of Physics, Indian Institute of Technology, Chennai-600 036, India.

 

Composites with compositions x Ba_0.8Pb_0.2TiO₃ + (1-x) Ni_0.5Zn_0.5Fe_1.95O_4-δ in which x varies as 1.0, 0.995, 0.990, 0.985, 0.980, 0.960, 0.940 and 0.920 in molar percent were prepared by the conventional double sintering method. Enough care was taken to compensate the evaporation of lead and zinc losses in the samples. The presence of two phases was confirmed by X-ray diffraction. These samples were prepared for their use as magneto-ferroelectric transducers and sensors.  The variation of ε′, tan δ were studied in the frequency range 100 Hz to 1 MHz at room temperature. AC conductivity data was evaluated at room temperature for all the compositions. Temperature variation of ε′, tan δ at 100 kHz and DC conductivity were measured in the temperature range 300 to 623 K.  The results are discussed in the light of polaran hopping mechanism. It is noticed that the presence of ferrite is drastically altering the ferroelectric behaviour of Ba_0.8Pb_0.2TiO₃ .

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PC-22                                                                                                                      43

A C CONDUCTIVITY AND DIELECTRIC PROPERTIES OF POLYETHYLENE OXIDE/POLYANILINE   COMPOSITES.

 

Devendrappa .H¹., U.V.Subba Rao² and  M.V.N.Ambika Prasad^3#.

 

¹Deptt. of Physics, Mangalore University Mangalore-574 199, India

²Deptt. of Physics, Osmania University Hyderabad-500 007, India

³Deptt. of Physics, Gulbarga University Gulbarga - 585 106, India.

Prasad1_Amb@rediffmail.com.

 

The polymer electrolytes based of PEO complexed with the conducting polyaniline (PANI) have been prepared in the different weight percentage ratios. The complexation is confirmed by X-ray and IR Spectroscopy. The A C conductivity and dielectric properties are studied by sandwiching pellets of these composites between the silver electrodes. The Impedance data’s are carried out by using FRA (AUTOLAB) in the frequency range 100Hz-1MHz. It is observed that the ac conductivity increases with the increase in frequency and temperature and is found to be constant upto 10⁴ kHz, because ions are tightly pinned to the polymer chain. However at higher frequencies, there is a significant increase in ac conductivity, which may be due to the strong hopping mechanism. The dielectric constant decreases with the increase in frequency and temperature. It is observed from the studies on dielectric loss, there is no significant loss at low frequency. However at high frequency, loss is more. These composites have extensive technological applications, in the field of Solid state batteries. 

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PC-23                                                                                                                      68

DIELECTRIC LOSS OF ARGON PLASMA TREATED PMMA

                                                                                                                                 

Raka V. Dabhade, Dept. of Physics, Fergusson College, Pune and

 

S. A. Gangal. Dept. of Electronic Science, University of Pune, Pune

 

The dielectric relaxation study can provide information about the segmental mobility of the polymer.  Dielectric relaxation is the result of movement of dipoles due to changing electric field in the frequency range 10² – 10¹⁰ Hz (1).  The relaxation behavior of polymers is related to their molecular structure and motion, the latter parameter being a function of temperature. The main modes of molecular motions are rotation of side groups and segmental motion due to which dielectric losses occur with a change in applied frequency and change in temperature.  Therefore macroscopic dielectric data over a range of frequency and temperature can provide valuable information on the structural behavior of polymers at a molecular level.

The difference in the structure of the commercially available linear PMMA  and argon plasma treated PMMA where cross linking and scissioning have taken place can lead to differences in the dielectric loss in the polymer (2).  According to Matasuguchi et al  the dielectric relaxation of a polymer arises from the segmental motion of the main chain and side chains (2).  If the cross linking reaction proceeds, the film becomes rigid and segmental motion of the main chain is depressed as a result the dielectric loss is lowered. On similar lines in the present study an attempt has been made to correlate the results of the dielectric loss of argon plasma treated PMMA with the structural changes in the polymer that might have occurred due to the plasma treatment.

The argon plasma treated PMMA  for 10/15 minutes showed an increase in the loss near the relaxation temperature, which can be attributed to more segmental motion of  the molecular backbone due to scissioning  of side chains. Samples treated for 5 minutes showed a lowering of the loss suggesting decrease in the mobility due to cross linking of the polymer  which has been   confirmed by FTIR.

References:  (1)  “Mauritz”  www.psrc.usm.edu/mauritz

(2)&   M. Matsuguchi et al, Sens. & Actu.  B34 (1996)349

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SESSION VIII

OTHER RELATED TOPICS

Thursday, November 25, 2004

02.00 P.M.   -    03.30 P.M.

 

 

I-20                                                                                            141

ELECTRO-OPTIC RESPONSES OF FERROELECTRIC

LIQUID CRYSTALLINE MATERIALS WITH

LARGE SPONTANEOUS POLARIZATION

 

K.K. Raina¹*, Praveen Malik¹, Pankaj Kumar¹ and Alexej Bubnov²

 

¹School of Phys.& Materials Sc., Thapar Inst. of Engg. & Tech., Patiala –147004.

²Institute of Physics, Academy of Sciences of the Czech Republic,

Na Slovance 2, 182 21 Prague 8, Czech Republic

pmalik100@yahoo.com, rainatietp@yahoo.com

 

A new ferroelectric liquid crystalline material containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit has been synthesised and studied for electro-optic properties. This material exhibits the chiral nematic phase as well as a broad range of ferroelectric chiral smectic C* phase with high spontaneous polarization. The material exhibits relatively high spontaneous polarization at room temperature. The electro-optic properties in planar aligned cell of thickness 7.5mm were studied and compared with low spontaneous polarization FLC mixtures (~20 nC/cm²). The calculated values of spontaneous polarization (P_s), switching time (t) and torsional viscosity (g ) were found to be 230 nC/cm², 1600 ms, and ~ 85.00 kg/msec for high spontaneous polarisation liquid crystalline material respectively.

 

Acknowledgement : Authors gratefully acknowledge the financial support by CSIR

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I-21                                                                                              116

DIELECTRIC RESONATOR AND ITS APPLICATION

AS STABLE FREQUENCY REFERENCE

 

N. D. Kataria

 

National Physical Laboratory, Dr K. S. Krishnan Road, New Delhi-110012

 

Dielectric resonators have been employed as stabilized frequency determining component for the development of low-phase noise oscillators that improves the performance of current radar, communication and metrological system. The aim of our project is to develop a low phase noise dielectric resonator oscillator (DRO at a frequency close to the Cs atomic clock hyperfine frequency ~ 9.192 GHz. For such applications resonator with high unloaded Q-value and almost zero temperature coefficient of frequency drift (TCF) is required. Low loss single crystal sapphire demonstrates remarkably high Q-value at low temperatures. Unfortunately, sapphire has TCF ~60 ppm/K that has limited its applicability for high stable frequency microwave oscillator. 

In this paper we discuss the various frequency-temperature compensation techniques that has already been proposed and tested. The experimental results on sapphire-rutile composite dielectric resonator and stack resonator are discussed as frequency determining element. The composite resonator consists of sapphire puck sandwich between two thin rutile discs and supported by two quartz rods in a cylindrical copper cavity and operated in the whispering gallery mode. The stack resonator consists of two dielectrics Ba₅Nb₄O₁₅ (BN) and 5ZnO-Nb₂O₅, having opposite TCF, placed on top of a sapphire rod in a cylindrical copper cavity and excited to TE₀₁₁ mode. The measured relative frequency of the stacked resonator with temperature becomes almost linear with decreased effective τ_f with the proper choice of the volume fraction of ZN. A prototype  feedback DRO was assembled using an amplifier, a phase shifter, an attenuator The phase noise of the oscillator measured at 92 K is -83 dBc/Hz at 10 KHz offset frequency.

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O-19                                                                                               80

MICROWAVE BAND GAP STRUCTURES AND THE EFFECT OF LINE DEFECTS ON MICROWAVE PROPAGATION

 

E.D.V.Nagesh¹, V.Subramanian¹*, V.Sivasubramanian² and V.R. K.Murthy¹

¹Microwave Laboratory, I.I.T. Madras, Chennai – 600 036.

Materials Science Division, IGCAR, Kalpakkam 603 102.

manianvs@iitm.ac.in

 

In this paper we report the microwave propagation through square and triangular lattices of PTFE (Poly Tetra Fluoro Ethylene) rods (e=2.1) of diameter 0.6 cm. Using plane wave method, the maximum gap to mid-gap ratio was attained at a lattice spacing of almost 1.0 cm for both the lattices and so the lattice spacing was chosen as 1.0 cm. The square lattice shows a band gap from 12.14 to 14.82 GHz (gap width of 2.68 GHz) with a mid-gap frequency of 13.48 GHz. The appearance of the band gap was correlated theoretically by using plane wave expansion method, which predicts a band gap with a mid-gap frequency of 13.14 GHz and a gap width of 2.04 GHz. Similarly, the triangular lattice of lattice spacing 1.0 cm shows a band gap experimentally at 14.48 GHz with a gap width of 3.20 GHz and theoretically the mid-gap was observed to be at 14.82 GHz with a gap width of 4.71 GHz. Line defects were created in both the square and triangular lattices and made in the form of Fabry-Perot resonators. The appearance of the resonant mode within the band gap with the creation of the defect is of importance and the variation in the resonant frequency in both the lattices was analysed in terms of the defect spacing of the resonators.

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O-20                                                                                          137

HUMIDITY SENSING BEHAVIOUR OF LANTHANUM DOPED BARIUM STANNATE SYSTEM

 

Shail Upadhyay

 

Department of Physics, Nagpur University, Nagpur – 440 033

 

A few samples in the system Ba_1-xLa_xSnO₃ have been synthesized by conventional solid state ceramic route. The AC resistivity and capacitance of the samples were measured  in the RH range 10 – 90 % using impedance analyzer HP 4192 A LF. It is observed that these materials are promising candidates for humidity sensor applications. Moreover they are better resistive sensor as compared to capacitive sensor.

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O-21                                                                                               37

IMPORTANCE OF DIELECTRIC ANALYSIS OF IONICALLY CONDUCTING POLYMER COMPOSITE FILMS

 

Awalendra K. Thakur

 

Department of Physics & Meteorology, I.I.T., Kharagpur – 721302

 

Conventionally, the dielectric phenomena (dispersion/absorption) have been observed to occur over a very wide range of frequency covering 10^-6–10¹² Hz. It has been interpreted to be occurring due either to dipole relaxation arising from reorientational motion of molecular dipoles or electrical conduction arising from the transnational motion of electric charges (electrons/ions). Studies of dielectric behavior of materials therefore assume lot of significance from both the fundamental and applications point of view. Dielectric studies on polymeric materials have drawn considerable attention over the years in view of their importance in modern technological applications such as dielectric anisotropy in optical switching processes and thin film solid electrolytes for battery applications. In addition, complete information on dielectric relaxation and dielectric loss spectrum provides substantial insight into the reorientational dynamics of the molecules making it convenient to understand and predict the mechanism of ion dynamics.

The present paper aims to emphasize the importance of the studies of dielectric properties of ionically conducting polymer composites. The complex permittivity analysis reveals the presence of dipole in the bulk material. The presence of dielectric relaxation peak due to dipoles such as ion pair in the conductive polymer composite has been observed to govern the local viscosity in the material that may be affecting the charge transport phenomena. Finally dielectric analysis has been shown to be an effective method to provide an insight in to the detailed mechanism responsible for ion transport in conductive polymer composite electrolytes. The silent features of these results are expected to be discussed in the talk.

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PC-24                                                                                                                      72

ACTIVATION ENERGY OF AZINES AND DRUG

METAL COMPLEXES

 

Revanasiddappa.M, Jogad. M.S.¹, Aravind.H. Dhamya¹ and Angadi.S.D*

 

Department of Chemistry, Gulbarga University, Gulbarga, Karnataka - 585 106.

¹Department of Physics, S.B. College of Science, Gulbarga, Karnataka  - 585 103.

revum@rediffmail.com

 

Synthesized metal complexes were characterized by various physico-chemical methods. All these complexes are analyzed stoichiometry of the type 1:2. These complexes are non-electrolyte in nature. The complexes of VO, ZrO, Mn, Fe, Co, Ni, Cu, Cd and Hg have been studied by various spectral methods viz, UV, IR, ESR and XRD. On the basis of spectral data results, the coordination complexes of azines and lansoprazole drug compounds to the central metal can take place through the donor sites. The electrical conductivity of azines and drug complex molecules are increases with raising the temperature from 373 to 523 K, which indicates the semi-conducting behavior. However, at lower temperature from 298 to 373 K they behave as insulators. The orders of activation energy for the metal complexes are Fe > Cu > Mn > Co > VO > Cd > ZrO > Ni > Hg.  

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PC-25                                                                                                                      40

ELECTROCHEMICAL RESPONSE OF PURE NICKEL

IN ACID MEDIUM

 

Meetu Walia and Gurmeet Singh

 

Department of Chemistry, University of Delhi, Delhi-110 007.

meetuwalia@yahoo.com

 

This work presents electrochemical results of nickel immersed in 1N H₂SO₄ and also in the presence of various phosphonium compound which act as corrosion inhibitor. Galvanostatic Polarisation, Potentiostatic Polarisation, Infrared Spectroscopy, and scanning electron microscopy were performed. Nickel is a silvery white transition metal that makes up 0.007 % of the earth’s crust. Nickel has a good resistance to many corrosive solutions like slightly acidic and alkaline solutions. Nickel forms a good base for alloys requiring strength at high temperatures. The corrosive environment in which nickel alloys can be used are varied; embracing acids, salts and alkalis, sea waters, natural water and atmosphere. Nickel occupies an intermediate position in the electrochemical series

E ⁰ Ni ²⁺ / Ni   =   - 0.25V. It is nobler than Zn and Fe but less than Sn, Pb and Cu

The inhibition of corrosion of nickel in H₂SO₄ solution by some Phosphonium compounds has been studied for different concentrations and temperatures in the presence of these inhibitors. The inhibition efficiency increases with increasing inhibitor concentrations. Polarisation studies indicate that the compounds used are all mixed inhibitors for nickel metal. By Potentiostatic Polarisation it had been concluded that nickel passivate in 1N H₂SO₄. Potentiostatic Polarisation studies also show that these compounds are good passivators in 1N H₂SO₄. Inhibition by these compounds, which resulted because of the adsorption on metal surface, was also studied and proved with the help of infrared spectroscopy. The results were also confirmed by surface morphological studies. From the paper these conclusions are made :

1.    The inhibition action of these organic compounds is due to their adsorption on the nickel surface through strong pp-dp interaction.

2.    The inhibition efficiency increases with increase in concentration of the inhibitors.

3.    ETPPI, PTPPB and HTPPB are mixed type of inhibitors.

4.    Inhibition efficiency increases with increase in temperature of system for all the concentrations of the inhibitors, which makes these additives as potential high temperature corrosion inhibitors for nickel surfaces.

5.    From potentiostatic studies it has been concluded that these inhibitors are strongly adsorbed over nickel surface and are good passivators in 1N H₂SO₄. This passivation depends on already absorbed anions of the medium.

6.    In the adsorbed infrared spectra of inhibitors, either the disappearance of certain peaks or shifting of some peak values to higher frequencies proved that the inhibitors were adsorbed over the adsorbing surface which ultimately leads to the corrosion inhibition in acid media.

7.      The SEM studies also show inhibition behavior of the inhibitors on Nickel in the following : HTPPB>PTPPB>ETPPI.

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PC-26                                                                                                                      73

STUDY OF FLUID STRUCTURE AND DIELECTRIC BEHAVIOUR OF DIETHYLAMINE IN POLAR LIQUIDS.

 

A.Kingson Solomon Jeevaraj, G.Parthipan,T.Thenappan and U.SankarDepartment of physics, Alagappa University, Karaikudi-630 003

aksj@rediffmail.com

 

The liquid structure can be studied by the correlation factors. The study of correlation factors provides information on solute-solute interactions and solute-solvent interactions. For polar liquids diluted in non polar solvents Kirkwood correlation factor (g) explains the molecular interactions. For pure polar liquids Onsager model is used to explain the fluid structure. For a mixture of binary polar liquids, either of the above models is not applicable. Some authors used kumbharkhane model to describe the molecular interactions between two polar liquids. Assuming that the correlation factors of two liquids are affected by the same amount, corrective Kirkwood correlation factor (g_r) is used to explain the solute-solvent interactions. Effective Kirkwood correlation factor (g^eff) is used to explain homogeneous and heterogeneous molecular interactions. The Bruggemann mixture formula of static permittivity has been modified for binary mixtures of polar liquids by considering non-linear behaviour of volume fraction of one polar component in another polar liquid.. The modified Bruggemann factor (a) gives information on solute-solvent interactions. The excess dielectric constant (ε^E) can give information on heterogeneous molecular interactions. Dielectric studies are carried out for the binary mixture of Diethylamine with (i). 2-Ethyl -1-hexanol (ii). Diisopropyl ether (iii). Diethyl ether (iv). Ethyl acetate at different temperatures, at various concentrations of the components A and B. The values of g^eff, g_r, a and  ε^E are calculated at different temperatures and concentrations, and are reported.

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PC-27                                                                                                                      23

MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF Al₂O₃ DOPED ZnO BASED VARISTOR CERAMICS

 

Abhilasha Srivastava, Radheshyam Rai and K.K.Verma*

 

Electronic Material Division, National physical Laboratory, New Delhi-1100012

* Dr.R.M.L.Avadh University, Faizabad

 

Varistors (variable resistor) ceramics have become technologically important because of their highly nonlinear electrical characteristics enabling them to be used as reversible solid state switches with large energy handling capabilities. Functionally, varistors are equivalent to a back-to-back zener diode and are typically used in parallel with circuits to protect them from voltage surges. In normal use they are subject to a voltage below their characteristic switch voltage and pass only a leakage current[1].  When the voltage exceeds the switch voltage, for instance, during a voltage transient or surge, the varistors becomes highly conducting and draws the current through it, usually to ground. When the voltage returns to normal, the varistors returns to its highly resistive state. The switch is reversible with little or no hystersis, it can degrades under electrical loading. In the pre-switch region, the varistors is ohmic, and the leakage current is temperature dependent. Above the switch voltage, two regimes can be identified: one highly nonlinear and the other at highest voltages, when the materials are again ohmic. In the nonlinear regime, the relation between current and voltage is often expressed in terms of a power-law:   I µ V^a  , where a is the nonlinearity exponent.

The original varistors ceramics were developed in the early 1930s to replace early selenium rectifiers for protecting telephone systems. In 1969s Matsuoka, [2] announced the development of varistors based on ZnO compositions. The basis for varistors characteristics is that electron transport across charged grain boundaries is voltage dependent[3]. The solid-state reaction techniques were used to obtain Al doped zinc oxide ceramics. Preliminary crystal structure and micro- structure of the compounds were studied using X-ray diffraction (XRD) techniques and Scanning electron Microscope (SEM). The XRD study of the compound shows that sample has the tetragonal structure. Detailed electrical studies of the samples suggest that they have very interesting behavior of the compound. The change in the values of the resistivity with Al concentration show very interesting behavior of the compound. Temperature dependence of dc resistivity has also provided some interesting features of the compound.

Reference:

[1] David R. Clarke, j. Am. Ceram. Soc. 82[3] (1999) 485-502.

[2] M. Matsuoka, T. Masuyama and Y. Iida  Jpn. J. Appl. Phys. 8 (1969) 1275-76.

[3] C. H. Seager and G. E. Pike Appl. Phys. Lettr. 35(9) (1979) 709-11.

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PC-28                                                                                                                      50

             SYNTHESIS, CHARACTERIZATION AND AC CONDUCTIVITY OF POLYPYRROLE/La₂O₃ Composites

 

T.K.Vishnuvardhan, V.R.Kulkarni*, M.Revanasiddappa,

C.Basavaraja and S.C.Raghavendra¹

 

Department of Chemistry, Gulbarga University, Gulbarga-585 106.

1Department of E &CE, Rural Engineering College, Bhalki-585 328.

vishnu33vardhan@yahoo.com

 

Conducting polymer composites are in fact some suitable composition of a conducting polymer with one or more oxide materials so that their desirable properties are combined successfully. Conducting polymer composites of Polypyrrole/lanthanum oxide (PPy/La₂O₃) composites were prepared by chemically polymerizing the pyrrole in presence of an oxidant (FeCl₃) and with La₂O₃. The La₂O₃ is varied in   five different weight percentages in PPy/La₂O₃ composites.  The Content of La₂O₃ is varied from  10% to 50%. Synthesized composites are characterized by infrared (IR) and X-ray diffraction spectroscopes (XRD).  The surface morphology of the composites is investigated by scanning electron microscopy (SEM).   Ac. conductivity of the compressed pellets depends on the concentration of La₂O₃ in PPy. The frequency dependent ac conductivity reveals that the La₂O₃ concentration in ppy is responsible for the  variation of conductivity of  the  composites.

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PC-29                                                                                                                      54

DIELECTRIC BEHAVIOUR AND CONDUCTION MECHANISM IN Mn SUBSTITUTED Mg -Zn FERRITES

 

U.R.Ghodake ^a, P.P Bakare ^b, S.R. Sawant^c,and   S. S. Suryavanshi^a

 

^aDepartment Of Physics, Solapur University, Solapur, Kegaon, Solapur-413 255.

^bCenter for materials characterization, National Chemical Lab., Pune-411008

^cDepartment Of Electronics, Shivaji University, Kolhapur-416004

urghodake@rediffmail.com , sssuryavanshi@rediffmail.com

 

Compositions having the general formula, Zn_o.4Mg_0.6-xMn_xFe₂O_4­ ,where x = 0.00,0.01,0.03,0.05,0.07,0.09,0.10,0.15,0.20,0.25 and 0.30 have been synthesized by using co-precipitation technique using oxalate precursors. The dielectric constant (Î`), complex dielectric constant (Î``), dielectric loss tangent (tand) and a.c.electrical resistivity (ρ<sub>a.c</sub>.) of Mn substituted Mg-Zn ferrites of various compositions have been studied in the frequency range of 20Hz to 1MHz. Plot of dielectric constant (Î`) vs. the frequency exhibit dispersion up to 10kHz, while dielectric constant (Î`) almost levels off beyond 10 kHz. The dielectric constant (Î`) for these Mn substituted Mg -Zn ferrites is roughly inversely   proportional to the square root of resistivity. From plot of ρ_a.c.Vs. Logf, it is clear that in the lower frequency region the a.c. resistivity (ρ_a.c.) increases with increase in composition parameter x, reaches a maximum value at x = 0.09 and for x > 0.10 it decreases.

The values of DE in paramagnetic region are different and greater than those for the ferrimagnetic region. This suggests that the process of conduction mechanism is affected by the changes in the magnetic ordering. The values of DE and resistivity goes on increasing with the increase in concentration of Mn²⁺ ions up to x = 0.10 and for x > 0.10, the values of DE and resistivity decreases. The values of DE lies between 0.24ev to 0.40ev, which indicates that conduction process is due to hopping of polarons.

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PC-30                                                                                                                      66

ELECTRICAL PROPERTIES OF Sb⁵⁺ SUBSTITUTED

LITHIUM FERRITE

 

Chongtham Shivaji,^* Sumitra Phanjoubam, H.N.K. Sarma, Laishram Radhapiyari⁺

 

^* R&D Division, Manipur Science & Technology Council, Imphal – 795 001

Physics Department, Manipur University, Canchipur – 795 003

⁺Solid State Physics Laboratory, Lucknow Road, Delhi – 110 054

 

Electrical properties such as d.c. resistivity and dielectric constant and dielectric loss tangent of Li_0.5+x Fe_2.5-2x Sb_x O_4­ ferrites (with x = 0.0, 0.10, 0.15, 0.20, 0.25 and 0.30) have been investigated as a function of composition, temperature and frequency. The d.c. resistivity of the system was observed to increase with the substitution level of Sb⁵⁺. While a decrease in the d.c. resistivity was observed with increasing temperature. Two slopes were seen in the plots of temperature versus resistivity for almost all the samples. Activation energies for low and high temperature regions were calculated from the slopes of the curves. The dielectric constant showed dispersion with frequency in the range of 100Hz to 1MHz. Resonance peaks were observed in tand versus frequency curves. The mechanisms involved in the processes are discussed in this paper.

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PC-31                                                                                                                    105

MICROHARDNESS OF THE A^IBⁱⁱⁱC2^VI TERNARY CHALCOPYRITE SEMICONDUCTORS

 

D.Sharma, G.S. Sharma, A.S. Verma and S.R. Bhardwaj

 

Department of Physics, B.S.A. College, Mathura-281004

An entirely new approach has been involved for the microhardness determination of ternary chalcopyrite of the type A^IBⁱⁱⁱC2^VI.  The proposed relation is derived in terms of atomic number of constituent atoms and homopolar gap for the chalcopyrite series.  A discussion has also been presented among the mniroghardness, atomic number of constituent atoms and homopolar gap of these compounds.

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PC-32                                                                                                                    128

DIELECTRIC PROPERTIES OF CU SUBSTITUTED Ni-Zn FERRITE PREPARED BY CITRATE PRECURSOR METHOD

 

Mukesh C. Dimri, Subhash C. Kashyap, A. Verma and D.C. Dube

Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016

 

O.P. Thakur and Chandra Prakash

Solid State Physics Laboratory, Timarpur, Delhi-110054

 

 

Ni-Cu-Zn ferrite is a useful material for the electronic devices, because of its lower sintering temperature and better electrical and magnetic properties than Ni-Zn ferrite. Ni_0.6-xCu_xZn_0.4Fe₂O₄ having x = 0 to x = 0.4 were prepared by the well-known citrate precursor method. The dielectric constant of these ferrites increases with addition of Cu upto concentration x = 0.2, and decreases on further increase of copper concentration. The dielectric losses are also lowest for this composition. These changes with the Cu substitution take place because of the substitution of Ni ions by Cu ions, which disturbs the balance between tetrahedral and octahedral sites. The effect of temperature on its dielectric constant and losses are discussed.

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PC-33                                                                                                                    129

INFLUENCE OF DOPING/HUMIDITY ON THE ELECTRICAL

AND DIELECTRIC PROPERTIES OF POLYANILINE.

 

Vandna Luthra^1*, Umesh Verma¹, Ajay.K . Arora² and R.P.Tandon³

 

¹ Dept. of Physics, Gargi College, Siri Fort Road, New Delhi-110049

² Dept. of Physics and Electronics, Keshav Mahavidyalaya, Keshav Puram, Delhi

³ Dept. of Physics & Astrophysics, University of Delhi, Delhi-110007

 

Polyaniline was synthesized by chemical oxidative polymerisation technique was further doped with various protonic acids. The effect of doping on the dielectric and electrical properties has been analyzed. The dielectric constant as well as electrical conductivity increases as a function of doping level. The effect of humidity on the electrical conductivity and dielectric constant has also been evaluated and this has been analysed in light of water as secondary dopant for this system. The effect of humidity has a reversible effect on electrical conductivity. The role of doping/humidity has been analyzed in order to understand the mechanism of charge transport.

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PC-34                                                                                                                    135

DIELECTRIC PROPERTIES OF Li-Sb FERRITES

Chongtham Shivaji,^* Sumitra Phanjoubam, H.N.K. Sarma,
Laishram Radhapiyari⁺, Chandra Prakash⁺

 

^* R&D Division, Manipur Science & Technology Council, Imphal – 795 001

Physics Department, Manipur University, Canchipur – 795 003

⁺Solid State Physics Laboratory, Lucknow Road, Delhi – 110 054

sumitrap@sancharnet.in

 

Dielectric properties such as dielectric constant (e¢) and dielectric loss tangent (tan d) of Li_0.5+x Fe_2.5-2x Sb_x O_4­ ferrites, 0.10£x£0.30 in the steps of 0.05 have been investigated as a function of composition, frequency and temperature. The dielectric constant showed dispersion with frequency in the range of 100Hz – 1MHz. Peaks are observed in the tan d versus frequency curves for almost all the samples. The temperature variation of dielectric constant for the different samples were studied at 10KHz in the temperature range from room temperature to 433K. Peaks were observed for all the samples. The peaks were seen to shift towards higher temperature region as the substitution level increases. The mechanisms involved in the processes are discussed in this paper.

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PC-35                                                                                                                    144

DIELECTRIC BEHAVIOUR OF UNIRRADIATED AND IRRADIATED M-TYPE HEXAFERRITES.

 

Balwinder Kaur, Monita Bhat, Ravi Kumar*, F. Licci**,

K.K. Bamzai, and P.N.Kotru

 

Dept. of Physics & Electronics, University of Jammu, Jammu – 180 006 (India)

* Nuclear Science Centre, New Delhi - 110067

** Instituto MASPEC – CNR, Via Chiavari 18/A, 43100 Parma, Italy

 

Hexaferrites with the magnetoplumbite or related structures are the most promising materials because of their strong magnetic anisotropy. Hexaferrites find wide technological applications in mm- wave frequency devices, magnetic memories, high-density recording medium. It is well known that irradiation of solids with energetic particle beams leads to creation of wide variety of defects. The Swift Heavy Ions (SHI) irradiation in magnetic oxides and ferrites have been studied to understand the damaged structure and the modifications on their physical properties during the last two decades. The 50 MeV Li³⁺ ion irradiation induced modification on dielectric behaviour of flux grown Pure and Ga – In substituted Strontium Hexaferrite have been studied. Dielectric analysis was carried out using fully automated HP4192A impedance analyzer. The samples were irradiated using Lithium beam of energy 50 MeV with different fluence rate at NSC, New Delhi. Dielectric studies of both irradiated and unirradiated samples have been carried out and the effect of irradiation is studied. The variation of dielectric constant e^/ for pure and substituted Sr-hexaferrite were studied as a function of frequency of a.c. field in the frequency range 1KHz to 10MHz from room temperature to 500⁰C. Dielectric constant is found to decrease with frequency, but increases with temperature for both pristine as well as irradiated crystals. The variation of tand with frequency shows cusps for all the samples. The variation have been explained on the basis of Koop’s phenomenological theory, concentration of Fe²⁺ and Fe³⁺ ions on octahedral sites and hopping frequency of electrons between Fe²⁺ and Fe³⁺. The results are described and discussed.   

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PC-36                                                                                                                    147

DIELECTRIC CONSTANT OF SUPERCONDUCTING MATERIALS AND ITS USE IN DEVICE MODELING

 

Vincent Mathew

Department of Physics, St. Thomas College Palai, Kerala – 686 574

vincentmathew@rediffmail.com

 

The dielectric function of superconducting materials is an issue of great importance. The dielectric constant, evaluated using the formula, e_eq(w)  =  e_r  -  j , provides a means of modeling superconducting medium for the analysis of devices and circuits. However, this definition does not satisfy the Kramer’s-Kroning criteria for causality and so it is non-physical. In this paper, a microstrip line with a superconducting layer in the substrate has been worked out, as an example of applicability of the above formula and numerical results are presented.

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PC-37                                                                                                                    161

SYNTHESIS AND CHARACTERIZATION OF

NOVEL ACRYLATE BASED SIDE CHAIN

FERROELECTRIC LIQUID CRYSTAL POLYMERS

 

G. Sumana¹, K.K. Raina¹*, P. Malik¹, P. Kumar¹, P. Sharma¹, S. Kapila¹,

A. Bubnov² and Chandra Prakash³

¹School of Physics & Materials Sc.,Thapar Inst.of Engg. & Tech., Patiala– 47004

²Institute of Physics, Academy of Sciences of the Czech Republic,

Na Slovance 2, 182 21 Prague 8, Czech Republic

³Electro ceramic group, Solid State Physics Laboratory, New Delhi, India

rainatietp@yahoo.com

 

Polyacrylate based side chain ferroelectric liquid crystal polymer was synthesized by reacting vacuum distilled hydroxy ethyl methacrylate and a chiral smectic C* liquid crystal Kr_8/12 having chemical structure

                                                                                 CH3

C₈H₁₇ O –       -COO -       -CH==CH -       p; -O-CO-C-C₁₂H₂₅

                                                                                                         OH

by irradiating the mixture using UV radiation for 15-20 minutes. The resulting polymer liquid crystal was analyzed by proton NMR. The phase transitions of the Kr_8/12 and the polymer were studied using optical polarizing microscope and differential scanning Calorimetry (DSC). Our results reveal a decrease in the transition of the liquid crystal phases after incorporating the polymer moiety. The material has shown the fast ferroelectric switching response. The dielectric permittivity and the electro-optic parameters have been measured as a function of temperature. The electro-optic properties of polymer ferroelectric liquid crystal were investigated and explained on the basis of their structure – property relationships.

Acknowledgement : Authors gratefully acknowledge the financial support by CSIR

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PC-38                                                                                                                    183

DESIGN AND DEVELOPMENT OF TEMPERATURE CONTROLLER CIRCUIT FOR H₂S GAS SENSOR APPLICATIONS

 

^dC Ghanshyam, Harsimrat Kaur*, Manbir Kaur*, Rahul Tripathy#, Sunita Mishra, N.Ram, Satinder Singh,  RP  Bajpai and RK Bedi

Microelectronics group, C.S.I.O., Sector 30-C, Chandigarh.

*Department of Electronics and Communication, GND Engg. College, Ludhiana

# DDU University of Gorakhpur, Gorakhpur (UP)

** Department of physics, Material Science Lab, GND University, Amritsar

 

Offensive oral odour is comprised of volatile sulphides such as methyal mercaptan (CH₃SH), dimethyal sulphide (CH₃SCH₃) and hydrogen sulphide (H₂S).The detection of bad breath is necessary to avoid social abhorrence and for taking timely remedial action. This calls for the development of low power solid state sensors using metal oxide thin films sensitive enough to detect low concentrations of H₂S and CH₃SH. These volatile gases respond to the sensors at different temperatures. So selectivity op these gases sensors can be controlled by varying the temperature. This paper discusses the design and development of temperature controller circuit for controlling the selectivity of H₂S gas sensor. It also deliberates on the signal condition circuit and display developed electronics.

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PC-39                                                                                                                    167

CHARGE INJECTION AND TRANSPORT IN BLUE ORGANIC LIGHT EMITTING BASED LITHIUM TETRA-

(8-HYDROXY-QUINOLINATO) BORON COMPLEX

R. R. Koireng, P.C.Agarwal, Lokendra Kumar*, M.N. Kamalasanan*,

Subhas Chandra* and R.P.Tandon^#

 

Dept. of Physics, Regional Institute of Education, Bhubaneswar(NCERT)-751022

*OLED Lab., National Physical Laboratory, New Delhi-110 012 (India)

^# Department of Physics and Astrophysics, Delhi University, Delhi-110007 karenk_r@yahoo.com

 

Blue electro luminescent materials are essential for the development of full colour display. In this paper, we report the charge injection and transport of blue emitter Lithium tetra- (8-hydroxy -quinolinato) boron complex for organic light emitting diode (OLED) applications. The boron complex was synthesized by the reaction of lithium borohydride with 8-hydroxyquinoline at room temperature and shows absorption cut off wavelength at 410 nm and bright blue photoluminescence (PL) with a peak wavelength at 485 nm. The optimum thickness of the layer was 50 nm and the thickness of the hole transport layer was 25 nm as measured by quartz crystal thickness monitor and I-V characteristics of bilayer OLED show highly non-linear nature with ohmic conduction at low voltages and trap charge limited conduction at high voltages. Devices with a 50 nm thick organic layer emitted blue light when a voltage of about 9 volts was applied across it.

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PC-40                                                                                                                    168

PHONON FREQUENCIES IN BULK METALLIC GLASS

 

P.C. Agarwal and R.R.Koireng

Dept. of Physics, Regional Institute of Education(NCERT), Bhubaneswar-751022.

pcagca@yahoo.com

 

Analytical expressions for the phonon frequencies of a ternary metallic glass, employing a simple model approach, are derived both for longitudinal and transverse modes of vibrations. Our model assumes a central force, effective between the nearest neighbours, and a volume dependent force. The computation of the phonon frequencies of the longitudinal and transverse phonons in Pd₄₀Ni₄₀Cu₂₀ bulk metallic glass is carried out for the first time both for self-consistent screening of conduction electrons with and without the inclusion of correlation effects. Phonon frequency expressions reproduce the main characteristic features of the dispersion curves.

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PC-41                                                                                                                    171

An approach on theoretical model of several trapping centres (TC) and recombination centres (RC) in thermoluminescence phenomenon

 

Hari Om Gupta

D.D.U. Gorakhpur University, Gorakhpur, Uttarpradesh-273009, India.

hoguptagkp@yahoo.com

 

Chen and Zimmerman have explained some important behaviours of thermoluminescence model involving TC and RC. We here further elaborated their work and generalised the thermoluminescence model (see figure) with several recombination centres (RC₁, RC₂, RC₃, ……RC_i) and trapping centres (TC₁, TC₂, TC₃,…….TC_j).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A large number of RC results in narrowing of peak, high activation energy and have high frequency factor value. Further it causes competition among RC, among TC and inbetween RC and TC.  Our aim is to distinguish these recombination centres and trapping centres so that any type of behaviour of a particular centre that comes in near future should be accommodated in it through large and useful number of variables involved in equations. We are also presenting the derived set of equations for irradiation, relaxation and heating phases for all the levels- valance band, conduction band, TC and RC along with TL intensity equations .

References:

1.                   R.Chen, P.L.Leung and M.J.Stokes, Radiation Measurements 32, 505-511(2000).

2.                   J.Zimmerman, J.Phys. C: Solid State Phys. 4, 3265-3276 (1971).

3.                   R.Chen and P.L.Leung, J.Phys. D: Appl. Phys. 33, 846-850 (2000).

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PC-42                                                                                                                     160

DIELECTRIC AND VARISTOR MECHANISM IN

ZNO VARISTOR

 

S. S. Husain¹, Ashutosh Shukla¹, N. P. Gupta² and R. P. Tandon³

¹Deapartment of Physics, GGD University, Bilaspur, Madhya Pradesh

²Ex-HOD, Physics, JV Jain College, Saharanpur, (UP).

³ Department of Physics and Astrophysics, University of Delhi, Delhi – 110 007

 

Zinc oxide varistors  are used as surge arresters to protect the electronic equipments against the high voltage spikes. In the present case ZnO-Bi₂O₃-Sb₂O₃ based systems were synthesized using mixed oxide route and sintering them at elevated temperatures. The sintered bodies were lapped, polished and cleaned ultrasonically before providing them with fire-on type silver paste. I-V characteristics of ZnO varistor devices resemble with back to back zener diodes but with far greater voltage current and power handling   capacity. Initially it stays almost insulating up to certain fixed voltage called breakdown field, E_br above which it becomes conducting. The log I-V characteristic is approximately linear and can be represented by the empirical relation (J₁/J₂)=(F₁/F₂)^a ,where a = 1 corresponds to an ohmic device and a ® ¥ shows perfect varistor. In the present case a was found to between 15-25 depending on sample. The mechanism underlying the varistor action can be associated with  grain-intergranular barrier junction. Most of the theoretical models  proposed so far to explain the varistor behavior are based on  grain-grain conductance while others  are based on the double depletion layer concept for the region of grain-grain contact which forms the basis. The presence of intergranular layers which are formed due to additives play an important role on the magnitude of breakdown voltage.

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PC-43                                                                                                                     163

DIELECTRIC PROPERTIES OF NOVEL SEMICONDUCTING GLASS FOR GAS SENSOR APPLICATIONS

 

Ashok Kumar¹, N. N. Swami², N. C. Mehera³ and R. P. Tandon⁴

¹Department of Physics, Eritrean Institute of Tech., Asmara, Eritrea (N.E.Africa)

²Ex-scientist, National Physical Laboratory, New Delhi – 110 012

³USIC, University of Delhi, Delhi – 110 007

⁴Department of Physics and Astrophysics, University of Delhi – 110 007

 

Recently great interest has been shown in the glassy gas sensors for oxygen detection. These sensor elements are inexpensive and easy to fabricate. In the present case we have investigated the system.V₂O₅-Sr₂O₃-B₂O₃. The glasses were obtained by melting a mixture of appropriate quantities of oxides at 950 ⁰ and quenching the melt. Samples were crushed and compacted into disc shaped samples using an organic binder. The test specimens were mounted in the standard test assembly having the provision of flow of oxygen gas. The measurement of sensitivity (S=R_g/R_o) was performed as a function of temperature and gas pressures. Most of the changes in conductivity occurred in the initial first few minutes followed by a gradual change. This could be explained on the basis of phenomenon of surface adsorption followed by bulk diffusion.

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PC-44                                                                                                              194

CORRELATION BETWEEN ELECTRONIC DIELECTRIC AND REFRACTIVE PROPERTIES OF THE BINARY SOLIDS

 

K.P.Tiwari¹ and K.K. Sarkar²

‘Department of physics, B.S.A College Mathura-281004, India

²Department of physics, St.John’s College Agra-282002, India

ajay_ phy@rediffmail.com

 

A recently proposed relationship between refractive index and energy gaps in binary solids has been critically examined and found to be disagreeing with experimentally measured values for simple binary solids .Thus, a new empirical ion dependent correlation is proposed which shows fine agreement with the measured values .The theoretical validity of this correlation is also established and further uses of this study are proposed. The whole study is also proposed to extend for the theoretical analysis of the properties of nano materials

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