Electric field dependence of characteristic temperatures in PbSc _0.5Ta_0.5O₃ and Pb_0.78Ba _0.22Sc_0.5Ta_0.5O₃ relaxors studied via acoustic emission

Two model relaxor ferroelectrics PbSc_0.5Ta_0.5O ₃ (undergoing a spontaneous para-to-ferroelectric phase transformation) and Pb_0.78Ba_0.22Sc_0.5Ta _0.5O₃ (no long-range ferroelectric order in the absence of an external electric field) were studied by acoustic emission in the temperature range 200-600 K under a dc field E. Both compounds exhibit a para-to-antiferroelectric transformation at T_n, which is slightly above the temperature of the dielectric-permittivity maximum. For both compounds the intermediate temperature T^* increases linearly with increasing E. The dT^*/dE slope is larger than that of the ferroelectric transformation temperature T_c, similar to the transformation phenomena in BaTiO₃. The T^*(E) increase is suggested to be due to enhanced dipole polarizations inside the polar nanoregions.