Thermally Induced Transitions And Depolarization Of Fe2o3 Doped Pmns-Pzn-Pzt Piezoelectric Ceramics

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 T-m is frequency independent, which rules out the ceramics to be classified as typical relaxors. Meanwhile, the depolarization temperature T-d determined by the thermally stimulated depolarization current is found to be notably lower than T-m, which is distinct from the behaviors of normal ferroelectrics as well. An extraordinary phenomenon noted is that the T-d 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.