(Bi_1/2K_1/2)TiO₃lead-free ferroelectric ceramics: Processing, properties, and compositional modifications

Bismuth potassium titanate (Bi1/2K1/2)TiO3 with an A-site complex perovskite structure is regarded as a promising lead-free ferroelectric/piezoelectric material. Studies on the fundamental properties of (Bi1/2K1/2)TiO3 have, however, been faced with difficulties in fabricating dense and phase-pure (i.e., "high-quality") bulk ceramics caused by its low melting point and the volatility of Bi and K. This paper reviews our findings on the fabrication process and fundamental properties of such high-quality (Bi1/2K1/2)TiO3 ceramics. After a brief survey on the crystal structure and physical/chemical stability of (Bi1/2K1/2)TiO3, our fabrication process of (Bi1/2K1/2)TiO3 ceramics utilizing the hydrothermal synthesis method is described. Then, the phase transition behavior of (Bi1/2K1/2)TiO3 is discussed based on the electrical and electromechanical responses of the high-quality ceramic samples. The last part of this paper presents two examples of compositional modifications of (Bi1/2K1/2)TiO3 ceramics aiming at developing dielectric and piezoelectric materials for use in capacitors and actuators.