Synthesis of Nondoped Potassium Niobate Ceramics by Ultrasonic Assisted Hydrothermal Method

Non doped potassium niobate (KNbO 3 ) 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 KNbO 3 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 KNbO 3 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 KNbO 3 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 k r and k t and the piezoelectric constants d 31 and d 33 were determined to be 0.17 and 0.28, and -31 and 51 pm/V, respectively.