Degradation of PZT-4D hard piezoceramics under moderate heating

The changes produced in the dielectric permittivity, the transverse piezoelectric coefficient, the k31 coupling factor, the s11E elastic compliance and the mechanical quality factor of PZT-4D hard piezoceramics by heating have been investigated. The ceramics were then repoled, and the reversible and irreversible components of the changes quantified. The results showed that depolarisation began at 150°C. A high level of poling was retained even after heating at 300°C (d31=−83×10−12 C N−1 and k31=0.225), only 20°C below the transition temperature. However, a significant irreversible degradation of the mechanical quality factor, Qm, occurred at a temperature as low as 100°C. Experiments on thinned specimens showed that the degradation of Qm took place in the Ag doped layer produced by the electrodes. Indentation surface cracks were also introduced into the ceramics to investigate the behaviour of cracks during the thermal treatments.