Synthesis and piezoelectric properties of KxNa1−xNbO3 ceramic by molten salt method

KxNa1−xNbO3 ceramic powder with perovskite structure was synthesized in molten salt with a Na2CO3/K2CO3 molar ratio of 1:1, under different salt-to-oxide weight ratios of 1:10, 1:5, 1:3, 1:2.5 and 1:2 in the temperatures range of 650–900 °C. It is found that the synthesizing temperature and salt-to-oxide ratios had significant effects on the morphology of KxNa1−xNbO3 powder. The X-ray diffraction analysis indicated that a pure perovskite structure of KxNa1−xNbO3 powder could be synthesized at 650 °C. The microstructure observation revealed that the crystal morphology of KxNa1−xNbO3 powder changed from spheroid to cube, and then became irregular after further increasing temperature. The grain size of the synthesized powder increased by an increment of the molten salt content. The KxNa1−xNbO3 ceramics were prepared at x = 0.345 by adding 1.0 mol% ZnO as sintering aid, and the optimized dielectric and piezoelectric properties are obtained as following: d33 = 120 pC/N, Tc = 406 °C, Qm = 126 and kp = 0.302.