Dependence of dielectric relaxation on ac drive in [Pb(Mg_1/3Nb_2/3)O₃](_1-x)-(PbTiO ₃)_x single crystals

Dielectric measurements under different ac drive voltages were performed on single crystals of (PbMg_1/3Nb_2/3O₃)(_1-x)(PbTiO ₃)_x [(PMN)_(1-x)(PT)_x] for 0≤x≤0.3. A significant increase in permittivity was observed with increasing ac drive for all compositions. The magnitude of increase depended on temperature and measurement frequency. Alternating current drive effects were found to be a low frequency phenomenon, primarily below 10⁶ Hz. Three distinct ac-drive amplitude ranges are believed to exist in which various types of contributions dominate in the dielectric relaxation: (i) a glassy mechanism is dominant at low drives and gives rise to the typical relaxor ferroelectric characteristics in the linear dielectric response, (ii) a kink or boundary vibration type which is dominant at intermediate drives and gives rise to the nonlinearities in the dielectric response of relaxors under moderate ac drives, and (iii) a domain wall motion type which is dominant at higher drives and results in polarization reversal.