Study on Microwave―assisted Hydrothermal Synthesis and the Properties of KNbO3 Powders

KNbO3 powders with different phases and morphologies were successfully synthesized through the reaction between KOH and Nb2O5 by microwave―assisted hydrothermal method at 200 . Pure KNbO3 crystals were obtained when the concentration of KOH was maintained from 10mol/L to 14mol/L. According to the XRD, FESEM and TEM characterizations, it could be observed that as increasing the concentration of KOH from 10mol/L to 15mol/L, the KNbO3 phases changed from rhombohedral to orthorhombic then to tetragonal, and the corresponding morphology of the KNbO3 powders changed from pyramid―like to rod―like then to cubic―like. Some Nb2O5 phases were found when the concentration of KOH increased to 15mol/L. KNbO3 ceramics were sintered from the KNbO3 powders by conventional processing. The piezoeletric properties such as the piezoeletric constant d33, the relative permittivity ε33/ε0, the dielectric loss tanδ, the electromechanical coupling factors kp and the mechanical quality factor Qm of the sintered KNbO3 ceramics were 80 pC/N, 302, 0.023, 0.17, 70, respectively. The tetragonal to orthorhombic and cubic to tetragonal phase transitions temperatures were 223 and 420 , respectively.