Piezoelectric relaxation and large anisotropy of modified lead titanate ceramics

In this study we investigate piezoelectric relaxation in Sm modified PbTiO₃ ceramics. The piezoelectric coefficients d₃₃ and d₃₁ were measured by a direct quasi-static method in the temperature range from 25 to 150°C and frequency range from >0.01 Hz to 100 Hz. The results show presence of huge piezoelectric relaxation for both d₃₃ and d₃₁, which change by factor of nearly two (d₃₃) and four (d₃₁) in the examined frequency range. The two piezoelectric coefficients show qualitatively similar behavior as a function of frequency. The piezoelectric anisotropy (d₃₃/d₃₁ ratio) of this material is found to be both temperature and frequency dependent. The maximum anisotropy is about 20 at room temperature and at 100 Hz. It decreases as the temperature increases or frequency decreases and finally it approaches at low frequencies the value typical for that in PZT ceramics (about 3).