Lead-free piezoelectric powders, K_0.5Bi_0.5TiO₃ (KBT), were synthesized by sol-gel, hydrothermal and sol-gel-hydrothermal methods, respectively. The structures and morphologies of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the pure perovskite KBT powders can be obtained by all three methods; however, the formation mechanism and morphology evolution of powders prepared by various processes are quite different. It was deduced that the solid diffusion mechanism was applied to sol-gel process. Due to the high-temperature treatment above 700 ℃, the KBT powders produced by sol-gel method had large size with serious agglomeration. The cubically shaped nanopowders were prepared by hydrothermal method, which belongs to dissolution-crystallization mechanism. The in-situ transformation mechanism was applied to sol-gel-hydrothermal process, and gel clusters played a crucial role in the formation of nanowire morphology.

Key words: K_0.5Bi_0.5TiO₃, sol-gel, hydrothermal, sol-gel-hydrothermal, nanowire