STUDY OF MODIFIED PZT/SBN ELECTROCERAMICS FOR DEVICE APPLICATIONS

Abstract

The excellent ferroelectric properties of PZT/PLZTISBN electroceramics continue to attract attention of the researchers for device applications. The present thesis is an effort in search of new modified PZT/PLZT/SBN electroceramic material which could meet the device demands. This thesis is mainly concerned with synthesis and characterization of the modified PZT/PLZT/SBN electroceramic. The effect of dopants (Ca, Fe, Sr, Mn modified PLZT, Y, Nb, Nd modified PZT and alkali modified SBN) on phase transition behavior, ferroelectric property, and crystal structure was explored, with the aid of x-ray diffraction, dielectric permittivity verses temperature, ferroelectric hysteresis loop and complex impedance analysis. The reaction kinetics and heating rate effects involved in the formation of PLZT by solid state reaction and its further effect on dielectric and ferroelectric properties were investigated which could be useful for the accurate design of processing plants in industries. Quantitative XRD technique carried out with NiO as internal standard shows that 320 kJ/mol activation energy is needed for the formation of PLZT composition and the best dielectric and ferroelectric properties were found for the sample heat treated at 1100 °C and at a heating rate of 6 °C/min. Fe and Ca modified PLZT was synthesized by solid state reaction technique using their mixed oxides. A new quantitative XRD analysis on intensity of XRD peak was carried out to study site occupation of Fe in ABO3 perovskite lattice of PLZT. From the detail study it was found that Fe occupied A site up to X0.06 and beyond x=0.06 it occupied both A & B lattice sites of PLZT. A remarkable observation of anti-ferroelectric like double loop was observed at higher Fe doping in PLZT, which suppressed the dielectric, pyroelectric and ferroelectric properties of the compositions. Ca doping had shown solubility up to x=0.015 limits and it does not show any change on dielectric and ferroelectric properties of PLZT. Mn and Sr modified PLZT were synthesized by coprecipitation and solgel techniques respectively and their phase formation was studied by DTA/TG and XRD analysis. Mn doping causes decrease in phase transition temperature and a remarkable increase in the dielectric constant. Detailed dielectric dispersion study was carried out to study the dispersion mechanism involved in PLZT. Domain reorientation dynamics study was carried out by analyzing the frequency dependence of backswitching and normalized coercive field on Sr modified PLZT. It was observed that Sr doping increases the percentage of backswitehing and decreases normalized coercivity, and it facilitates ferroelectric switching which can be used for making switching devices. Lio.sNao.5, Lio.5K0.5 and Rb modified SBN compositions were synthesized by solid state reaction, coprecipitation and sol-gel techniques respectively and phase formation was confirmed by DTA/TG and XRD analysis. All the alkali doping had shown an increase in phase transition temperature along with fall in dielectric constant of the synthesized materials. A unidirectional growth of grains was observed in all the alkali modified SBN, which are expected to be due to the lowering of sintering conditions with alkali doping. The detailed study of frequency dependent P-E loop was done to study the effect of 90 degree domain in the ferroelectric properties of Lio5K0.5 modified SBN. Best fatigue behavior was observed in X0.12 doping of Lio.5K0.5 in SBN. Yttrium and and Nb, Nd modified PZT were synthesized by coprecipitation and solid state reaction technique respectively. Phase formation was confirmed by DTA/TG and XRD techniques. An increase in dielectric constant with decreasing phase transition temperature along with large increase in remnant polarization was observed with Yttrium doping in PZT composition. Detailed a.c conductivity dispersion study was carried out to know the conduction mechanism in PZT material. Effect of lead zirconate environment during sintering on the structural properties of PZT was also analyzed. Detailed analysis of impedance spectroscopy was carried out on Nd, Nb modified PZT to investigate the grain/grain-boundary resistance dependence on temperature and dopants. Also thermodynamic properties of the material such as enthalpy, Gibb's free energy and entropy were calculated using impedance spectroscopy data. The detailed conclusions and recommendations are given in Chapter 8.