Characterization of piezoelectric materials using ultrasonic and resonant techniques

Resonance technique for determining the physical properties of piezoelectric material can be difficult to implement for some low symmetry systems. Inconstancy may be introduced because several samples are needed and the degree of poling depends on sample geometry. The ultrasonic method on the other hand, allows the determination of a complete set of elastic, piezoelectric, dielectric constants for materials of certain symmetries. However, some of these independent constants can not be directly measured from the phase velocities of pure modes, they need to be derived by solving a complicated coupled Christoffel equation, some relatively large errors may be introduced into these derivations. We found that if an additional length-longitudinal vibrator is used to assist the measurements, the computation would be greatly simplified and the final results became more accurate. As an example, the elastic, piezoelectric, dielectric constants and electromechanical coupling factors have been determined for a PZT-5H piezoelectric ceramic by using the combined method. This method can also be extended to piezoelectric crystals with symmetry point group of 4mm and 3mm. Keyword: Ultrasonic measurement, resonance, piezoelectric ceramic, PZT-5H, Christoffel equation, elastic constant, piezoelectric constant, dielectric constant, electromechanical coupling factor.