The Optic Frequency Dielectric Spectrum And Low Frequency Dielectric Properties Study For Typical Perovskite Ceramics

The dielectric spectrum measurement for the condensed materials can combine the microscopic parameters and macroscopical physical quantity which can be measured, therefore it can do the effective study on the charge movement, shortrange interaction, interface polarization and the relevant laws on structure. The research on dielectric spectrum can make the connection on the macroscopical properties theory and mesoscopic, nanoscopic, microscopic structure, explore to build the theoretical model on the relevance of’microscopic structure——mesoscopic structure——macroscopic properties’, which can provide theoretical basis for dielectrics research and engineer design.Firstly, for the optical dielectric spectrum research, the pseudo-potential plane wave method and the generalized gradient approximation (GGA) have been used to calculate the electronic structures and optical dielectric spectums of cubic BaTiO3(BT), PbTiO3(PT), and PbZrO3(PZ), respectively. The dielectric constant imaginary parts (ε2(ω)) of these three materials have been analyzed with the optical transition theory. Furthermore, the82(ω) peaks have been fitted by Lorentz formula and the fitting results were discussed with the population analysis.For the low frequency dielectric spectrum research, PZT95/5ceramic by Sol-Gel process was tested for dielectric spectrum including the dielectric spectrums for temperature and frequency, the results showed that the sample has large and stable dielectric constants (103-104) in the wide temperature range and piezoelectric effect occurred in electrical frequency range for industrial application. The dielectric relaxation for the sample is not typical Debye model but the many-body model on relaxation polarization.PZT95/5films by Sol-Gel process was tested for dielectric spectrum including the dielectric spectrums for temperature and frequency, respectively, the results showed that the transition peak of ε(T) curve got broad and flat with increasing frequency and the ε-1(T) curve at high frequency didn’t obey the Curie-Weiss law. The ε(f) curves with different temperatures were fitted by the universal relaxation law, obtaining the exponent n(T) curve. The n(T) curve was discussed combining the change in microstructure with the AFE-FE-PE transition process.PLZT7/40/60film by Sol-Gel process was tested for dielectric spectrum including the dielectric spectrums for temperature and frequency and the AC conductivity. The results show that:the sample has the relaxation ferroelectric character, which has dispersion phase transition and there are oxygen defects in the film sample. Through the fitting of experimental curves in different temperatures which used Cole-Cole empirical equation. The temperature functions on the dielectric constant, most probable relaxation time, fitting parameter h were analyzed combined with the relaxation ferroelectric feathers. And it was found that these curves have abnormal feathers in Tm and100℃～110℃, showing the crystal structure change within the material.