Extrinsic contributions to the low frequency piezoelectric properties of Ca/Sm modified lead titanate ceramics

The contribution of different mechanisms to the piezoelectric properties of modified lead titanate ceramics (Ca, Sm modifiers) have been studied by measuring the coefficient d(31), the phase angle, Phi, between the piezoelectric response and the applied mechanical force, and the dielectric constant epsilon(33) as a function of frequency (10(-2)-10(2) Hz) and the poling electric field. Extrinsic contributions from microstructure and space charge can be distinguished on the basis of these measurements, because results show the predominance of each one depending on grain size, poling process and measuring frequency. These contributions have the same sign as the intrinsic ones, and the change of sign that takes place in the phase angle and d(31)'' in PCT sample, must be related with the biphasic character of this ceramic when microcracks that modify the interaction between dielectric and elastic properties are present.