Poling Field Dependence of Longitudinal and Transverse Wave Velocities, Young's Modulus, and Poisson's Ratio in Piezoelectric Ceramics

Abstract

The longitudinal and transverse wave velocities in lead zirconate titanate (PZT), lead titanate, and lead-free ceramics vs DC poling fields were measured using an ultrasonic precision thickness gauge with high-frequency pulse oscillation to evaluate elastic constants, such as Young's modulus and Poisson's ratio. With the enhancement of domain alignment with the increase in poling field, the longitudinal wave velocity increased and the transverse wave velocity decreased independently of the ceramic composition. It was found that there was an important factor for obtaining a high piezoelectricity regarding Young's modulus and Poisson's ratio, that is, the low Young's modulus and high Poisson's ratio in the cases of PZT, alkali bismuth titanate, and alkali bismuth barium titanate with morphotropic phase boundaries (MPBs), and alkali niobate without MPBs. Furthermore, the increase in planar coupling factor corresponds to the increase in Poisson's ratio at all compositions including lead-containing and lead-free ceramic compositions. It was possible to divide the ceramics on the basis of longitudinal and transverse wave velocities into three groups, namely, PZT and lead titanate modified by 2.5 mol % lanthanum, alkali bismuth titanate and lead titanate modified by 10 mol % lanthanum, and alkali niobate.