DIELECTRIC BEHAVIOR OF LEAD MAGNESIUM NIOBATE RELAXORS

The dielectric behavior of a solid solution, 10 mol % lead titanate in lead magnesium niobate, is measured at different frequencies from 100 Hz to 100 kHz in the temperature range from -100 to 120 degrees C. A standardizing method is introduced to analyze the curve of the dielect ric constant vs temperature. It results a master curve behavior betwee n the dielectric constant and temperature at temperatures higher than the temperature of the dielectric constant maximum. The dielectric rel axation behavior is analyzed with various models. The best way to char acterize the degree of the dielectric relaxation for relaxor ferroelec trics is established using the experimental data. It is indicated that the temperature dependence of the static dielectric constant can be w ell described by an exponential function, while the temperature depend ence of the relaxation time is described by a superexponential functio n. Based on the specialty of the relaxer ferroelectrics, a distributio n function for the relaxation times is introduced and a model is intro duced to simulate the dielectric behavior of the relaxor ferroelectric s. The model can express well both the temperature and frequency depen dence of the dielectric behavior for a relaxor ferroelectrics. All of the parameters in the fitting formula can be experimentally determined . The model shows that in the low-temperature range, there are two sim ple relationships about the dielectric frequency spectrum: epsilon ''( omega,T)=(-pi/2)partial derivative epsilon'(omega,T)/partial derivativ e ln omega and epsilon'=B(T)(ln omega(0)-ln omega). These relationshi ps are verified by the experimental results. A way to obtain the accur ate value of epsilon(infinity) in the low-temperature range is describ ed.