Hydrothermal Solvothermal Synthesis of (K,Na)NbO_3 Lead-free Piezoelectric Ceramics and Its Properties

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 sinter-ing 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 solu-tions,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 K0.22Na0.78NbO3 exhibites high piezoelectric con-stant up to d33 = 120 pC/N,which is equivalent with the specimen of(K0.5,Na0.5)NbO3 synthesized by traditional solid-state reaction method.Therefore,it can be forecasted that the(K0.5,Na0.5)NbO3 ceramic sintered from the pow-ders synthesized by hydrothermal-solvothermal method will acquire higher piezoelectric property.