Hydrothermal synthesis of sodium and potassium niobates fine particles and their application to lead-free piezoelectric material

Cubic-shaped potassium and sodium niobates fine particles with orthorhombic crystal structures were successfully obtained by two-step hydrothermal reaction at 100°C for 24 h and 150-250°C for 3 h using a highly concentrated KOH or NaOH aqueous solution and a niobium pentachloride aqueous solution. The particle mean sizes were gradually controlled by changing the initial KOH and NaOH concentrations. Preheating of the precursor solution at 100°C for 24 h played an important role to obtain the desired alkali metal niobates fine particles with flat and smooth surfaces. The present potassium niobate fine particles exhibited good sintering property keeping with the original particle size and shape. Furthermore, thus obtained KN ceramics showed high piezoelectric properties.