Thermally induced transitions and depolarization of Fe2O3 doped PMnS-PZN-PZT piezoelectric ceramics

Abstract

Thermally induced transitions and depolarization of Fe2O3 doped PMnS-PZN-PZT ceramics are investigated. The ceramics have a highly diffused dielectric peak, but the temperature for the maximum dielectric permittivity Tm is frequency independent, which rules out the ceramics to be classified as typical relaxors. Meanwhile, the depolarization temperature Td determined by the thermally stimulated depolarization current is found to be notably lower than Tm, which is distinct from the behaviors of normal ferroelectrics as well. An extraordinary phenomenon noted is that the Td coincides quite well with a characteristic temperature where the dielectric permittivity shows the fastest increase. This characteristic temperature, denoted as TF-R, is faint in the temperature-dependent dielectric permittivity but can be well resolved by taking the first derivative of dielectric permittivity with respect to temperature. In addition, it is found a number of features of the anomaly around TF-R that are quite similar to the ferroelectric-to-relaxor transition in typical relaxors, and therefore, the TF-R is assigned to a transition from ferroelectric state to a “relaxor-like” state, in which the correlation of ferroelectric order could be weakened. Complex impedance analysis reveals the presence of small polarizable entities at high temperature, providing further support for the high-temperature relaxor-like state. It is suggested that the depolarization of Fe2O3 doped PMnS-PZN-PZT is related to the disruption of long-range ferroelectric order into polar regions with small sizes, rather than the ferroelectric-to-paraelectric transition.