Synthesis of Nondoped Potassium Niobate Ceramics by Ultrasonic Assisted Hydrothermal Method

Abstract

Non doped potassium niobate (KNbO3) crystal powders were synthesized by ultrasonic-assisted hydrothermal method for use in lead-free piezoelectric ceramics. By using the ultrasonic assist technique, the yield constant of the KNbO3 crystal powders became 96% with 3 h of reaction time. It was 4 times faster than that of the previous non ultrasonic assist hydrothermal method for the KNbO3 crystal powders. This result indicated that the high-intensity ultrasound radiation was effective for overcoming the serious problem of slow hydrothermal reaction. The reaction temperature was 190 °C, which was 20 °C lower than that of previous hydrothermal method. After sintering of hydrothermal KNbO3 powders at 1030 °C for 1 h, the obtained ceramics pellet was characterized by admittance measurement, and the piezoelectric performance was examined. From the admittance measurements corresponding to the radial and thickness vibration modes, the coupling factors kr and kt and the piezoelectric constants d31 and d33 were determined to be 0.17 and 0.28, and -31 and 51 pm/V, respectively.