Phase evolution of (K, Na)NbO 3 powder prepared by high temperature mixing under hydrothermal conditions

Abstract

(Na, K)NbO 3 (KNN) powders were successfully prepared by high temperature mixing method (HTMM) under hydrothermal conditions to study the effect of reaction time on the formation of KNN for three K +/(K + + Na +) ratios of 0.6, 0.7 and 0.8. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), to show the change of phase and morphology of the as-prepared particles with the K +/(K + + Na +) molar ratio in the solution. Pure Na-rich KNN monoclinic phase and pure K-rich KNN orthorhombic phase could be obtained quickly after mixing the solutions at high temperature when the K +/(K + + Na +) molar ratio was either 0.6 or 0.8. When the K +/(K + + Na +) molar ratio was 0.7, however, the K-rich KNN orthorhombic phase grain formed first, followed by the Na-rich KNN monoclinic phase grain, with the two phases coexisting in the final product.