Optimization of conditions of the synthesis of textured (Bi_(0.5)K_(0.5))TiO_3 piezoelectric ceramics by a reactive templated grain growth method

摘要

Piezoelectric ceramics have been widely used in various applications such as sensors, actuators, and transducers. Owing to the environmental concerns for the toxicity of lead, lead-free piezoelectric ceramics have been extensively studied, among which bismuth potassium titanate (Bi_(0.5)K_(0.5))TiO_3 (BKT) piezoelectric ceramic is one of the promising candidates because of its relatively high Curie temperature (T_c～400℃), high depolarization temperature (T_d～300℃), and a relatively high piezoelectric constant d_(33) of 125 pC/N. However, the d_(33) value is not sufficient for practical actuators and the d_(33) needs to be enhanced. Besides, BKT itself being the promising lead-free candidate, it is also important as end member for a variety of solid solutions like BKT-BaTiO_3, BKT-(Bi_(0.5)Na_(0.5))TiO_3, BKT-BaTiO_3-(Bi_(0.5)Na_(0.5))TiO_3, and so on. The grain-orientation imparted by the (001)/(100)-oriented BKT ceramics to the BKT-based solid solutions with crystal symmetry other than the tetragonal system could yield significant properties enhancement due to domain engineering. And, for the preparation of textured BKT ceramics, plate-like H_(1.08)Ti_(1.73)O_4.nH_2O (HTO) were used as template particles owing to their uniform-morphology with high aspect ratio. In this study, we focused on optimization of preparation conditions for the synthesis of (001)/(100) oriented BKT ceramics, using HTO-Bi_2O_3-KHCO_3 and HTO-TiO_2-Bi_2O_3-KHCO_3 reaction system. The matrix TiO_2 particles were used in the second reaction system beside the HTO template particles because the ratio of the matrix to the template particles strongly affects the grain orientation of the RTGG-processed ceramics.