Hydrothermal Synthesis and Microwave Sintering of (K0.5Na0.5)NbO3 Ceramics

Abstract

Lead-free piezoelectric ceramics of (K0.5Na0.5)NbO3 (KNN) were produced by using hydrothermally synthesized KNbO3 (KN) and NaNbO3 (NN) powders in a microwave furnace to reduce the volatilization of the alkaline elements. The KNN ceramics were synthesized by using a hydrothermal KN and NN mixed powder, a 1 mol% CuO-added hydrothermal KN and NN mixed powder and KNN calcined at various temperatures. The hydrothermal KN and NN powder and the calcined KNN powder had a pure perovskite phase while KNN ceramics with 1 mol% CuO showed a pyrochlore second phase. The CuO-added KNN ceramics sintered at 1050 degrees C for a short sintering time of 5 min at a fast heating rate of 50 degrees C/min to prevent evaporation of K2O and Na2O showed the highest piezoelectric properties (d(33) = 89 pC/N and k(p) = 0.28). The X-ray diffraction and the scanning electron microscopy results indicate that fast heating and short sintering time can affect the phase formation sequence in KNN ceramics.