Abstract: Hydrothermal-solvothermal method was used to synthesize (K, Na)NbO₃ powders with the addition of isopropanol. The influence of mineralizer concentration, reactive materials concentration on the phase, particle size, morphology and chemical composition of the products were investigated. The obtained powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscope (SEM). Then, the obtained (K, Na)NbO₃ powders were used to fabricate lead-free piezoelectric ceramics using the traditional sintering process, and its piezoelectric property was also studied. The results indicate that the pure (K, Na)NbO₃ powders with perovskite structure were successfully synthesized by hydrothermal-solvothermal method with the mineralizer solution concentration of 2mol/L and the addition of isopropanol. With increase of K+ content in the starting solutions, K+ content in the products also increased. The K/(K+Na) molar ratio in the products is lower than that in the staring solutions. Moreover, the specimen with the composition of K_0.22Na_0.78NbO₃ exhibites high piezoelectric constant up to d₃₃ = 120 pC/N, which is equivalent with the specimen of (K_0.5,Na_0.5)NbO₃ synthesized by traditional solid-state reaction method. Therefore, it can be forecasted that the (K_0.5,Na_0.5)NbO₃ ceramic sintered from the powders synthesized by hydrothermal-solvothermal method will acquire higher piezoelectric property.

Key words: (K, Na)NbO₃, hydrothermal-solvothermal method, isopropanol, piezoelectric property, lead-free