Polarization responses in lead magnesium niobate based relaxor ferroelectrics

Changes in the electrostrictive coefficients Q_ij , especially the volumetric coefficient, with temperature and bias field provides important information regarding the nature of the polarization in lead magnesium niobate based relaxor ferroelectrics. We show that the polarization response at temperatures near the dielectric constant maximum is mainly through the polar-vector reorientation of the nanopolar regions, as suggested by the polar glass model. As the temperature is lowered through the freezing transition, the polarization response is governed by the phase switching and intrinsic contributions rather than by the domain wall motions found in normal ferroelectrics.