Development of Environmental-Friendly Lead-Free Piezoelectric Materials for Actuator Uses

We have currently investigated the piezoelectric properties of bismuth tungstate, Bi2WO6 (BWO), mono-domain crystals and baium titanate, BaTiO3 (BT), based ceramics for use at high temperature. For BWO, the crystals grown by a slow cooling technique were characterized. The resonance response revealed that the BWO crystals maintained their piezoelectricity up to 400°C. In the solid solution ceramics of the BT-(Bi1/2Na1/2)TiO3 (BNT) system, we disclosed that the Curie temperature T c can be controlled from 130 to approximately 220°C. BNT-substituted BT ceramics showed a low temperature dependence of the piezoelectric constant up to 160°C. We also synthesized (K,Na)NbO3–LiNbO3–CuO leadfree piezoelectric ceramics that show a high mechanical quality factor Q m of 1400, a high d 15 of 207 pC/N, and a high k15 of 0.72. Using the shear vibration mode of the ceramics, an ultrasonic motor driven with four piezoelectric ceramic plates was developed. The highest revolution speed of 486 rpm was achieved at 34.5 kHz with the input voltage of approximately 180 Vp-p (peak to peak).