Dielectric nonlinearity of relaxor ferroelectric ceramics at low alternating-current-drive amplitudes

The dielectric nonlinear response of (PbMg_1/3Nb_2/3O₃)_0.9(PbTiO₃)_0.1 (0.9PMN-0.1PT) relaxor ceramics was investigated under different ac-drive voltages. It was observed that: (i) the dielectric permittivity is independent of the ac-field amplitude at high temperatures; (ii) with increasing ac-drive amplitude, the permittivity maximum increases, and the temperature of the maximum shifts to lower temperature; (iii) the nonlinear effect is weakened when the measurement frequency increases. The influence of increasing ac-drive amplitude was found to be similar to that of decreasing frequency. It is believed that the dielectric nonlinearities of relaxors at low drive amplitudes can be explained by the phase transition theory of the ergodic space undergoing a succession of shrinkages. A Monte Carlo simulation was performed on the flips of micro-polarizations at low ac-drive amplitudes to verify the theory.