Ferroelectric Domain Controlled Piezoelectric Ceramics and Their Devices for Environmental Friendly Materials

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Material research and development on piezoelectric ceramics was proposed from viewpoints of relationships between piezoelectricity and elastic constants such as Young's modulus and Poisson's ratio. We developed a method to be convenient to measure acoustic wave velocities by an ultrasonic thickness gauge with high-frequency. From the relationships between kp (planar coupling factor of disk) vs longitudinal and transverse wave velocities, Young's modulus and Poisson's ratio, the kp lineally increased with decreasing Young's modulus and with increasing Poisson's ratio. It was clarified that higher kp values can be realized in lower Young's modulus, higher Poisson's ratio and lower bulk density for lead-free ceramics. Furthermore, the candidates of lead-free ceramic compositions with higher piezoelectricity were proposed. The measurement of sound velocities was an effective method for researching and developing piezoelectric materials.