Temperature-dependent mechanical depolarization of ferroelectric ceramics

Mechanical depolarization of poled lead titanate zirconate (PZT) ceramics was conducted at a series of temperatures from 25 to 180 degrees C in a temperature-controlled silicon oil tank. Both the longitudinal strain and polarization of the bar-shaped PZT samples were measured during uni-axial compression up to 400 MPa. It is found that both the stress-induced switchable polarization and the switchable strain of the poled PZT samples decrease steadily with increasing temperature. Unpoled PZT samples were also tested and the switchable strains follow a rule similar to the poled ones but of smaller magnitude. By measuring the P-E hysteresis loops, polarization variations and strain variations of a compression-free, poled PZT sample during a full cycle of heating-cooling, it is found that at elevated temperatures, the reduced switchable polarization by stress is caused by the pyroelectric effect and the reduced switchable strain is mainly due to the decreasing tetragonality (c/a). Furthermore, it was found that both the poled and unpoled PZT ceramics show a recoverable thermal shrinkage effect within the measurement temperature range.