Piezoelectric relaxation and large anisotropy of modified lead titanate ceramics

In this study we investigate piezoelectric relaxation in Sm modified PbTiO/sub 3/ ceramics. The piezoelectric coefficients d/sub 33/ and d/sub 31/ were measured by a direct quasi-static method in the temperature range from 25 to 150/spl deg/C and frequency range from >0.01 Hz to 100 Hz. The results show presence of huge piezoelectric relaxation for both d/sub 33/ and d/sub 31/, which change by factor of nearly two (d/sub 33/) and four (d/sub 31/) in the examined frequency range. The two piezoelectric coefficients show qualitatively similar behavior as a function of frequency. The piezoelectric anisotropy (d/sub 33//d/sub 31/ 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).