Pinning and depinning mechanism of defect dipoles in PMnN-PZT ceramics

The frequency and temperature dependences of the hysteresis loops in Pb[(Zr_0.52Ti_0.48)_0.95(Mn_1/3Nb _2/3)_0.05]O₃ ceramics have been nvestigated. The polarization-field hysteresis curves show 'pinched' shapes at room temperature and higher frequencies, whereas they display normal square-like loops at 200°C and frequencies lower than 10mHz. Critical ferroelectric features such as the coercive field, polarization and internal bias field show a strong frequency or temperature dependence. The close relations between the P-E loops and the applied frequency and temperature indicate that the defect dipolar moment may change its magnitude with variation of the frequency or temperature. Comparing with the intrinsic depinning procedure induced by the changes in the distribution of defect dipoles, we provide new evidence for an extrinsic depinning mechanism of the defect dipoles in the bulk ceramics.