Temperature dependence of the dielectric constant of relaxor ferroelectrics

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Abstract
The temperature dependence of the dielectric constant under different frequencies is measured and analyzed for two different relaxor ferroelectrics, the solid solution ceramics of lead magnesium niobate and lead zinc niobate, respectively. Compared with the experimental results, the disadvantage of simulated results from different methods about the temperature dependence of the dielectric constant for relaxors is given. Based on this and the general behavior of the temperature dependence of the dielectric constant at both high and low temperatures, it is assumed that there are two kinds of polarization processes in the relaxor ferroelectrics. One of the polarization processes is associated with the thermally activated flips of the polar regions in the materials. Thus, a set of formulas is proposed to fit the temperature dependence of the dielectric constant at different frequencies. The formulas are strictly certified with the measured data of both materials. The formulas can fit the measured relation with high precision. The fitted results confirm and/or show the following: (1) The dielectric behavior at high temperatures is mainly contributed from a relaxation polarization process, which is associated with the thermally activated flips of polar regions in relaxor ferroelectrics. (2) The dielectric behavior at low temperatures is mainly contributed from the other polarization process. The frequency dependence of the dielectric constant shows that this process is something like a resonance polarization in the materials. (3) The dielectric behavior at temperatures around the temperatures of the dielectric constant maximum is determined with both polarization processes. The micro-origin of the resonance polarization is discussed with the breathing of frozen polar region in the materials. Based on the breathing model, all of the characteristics of the resonance polarization are explained. The amplitude dependence of the dielectric constant for relaxor ferroelectrics is also explained with the breathing model.