Large piezoelectric constant and high Curie temperature of lead-free piezoelectric ceramic ternary system based on bismuth sodium titanate-bismuth potassium titanate-barium titanate near the morphotropic phase boundary

A lead-free piezoelectric ceramic ternary system based on bismuth sodium titanate, (Bi1/2Na1/2)TiO3 (BNT) - bismuth potassium titanate (Bi1/2K1/2)TiO3 (BKT) - barium titanate BaTiO3 (BT) near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases has been investigated. In the case of a(Bi1/2Na1/2)TiO3-bBaTiO(3)-c(Bi1/2K1/2)TiO3 [BNBK(100a/100b/100c)] solid solution ceramics, the highest piezoelectric constant d(33) = 191 pC/N, Curie temperature, T-c = 301degreesC, electromechanical coupling factor, k(33) = 0.56 and dielectric constant, epsilon(33)(T)/epsilon(0) = 1141 are observed for the BNBK(85.2/2.8/12) composition which has a tetragonal phase near the MPB. The d33 value is the highest so far reported for all lead-free piezoelectric ceramics with T-c > 300degreesC. The BNT-BKT-BT ternary ceramics system sintered at 1200degreesC for 2h in air has a pure perovskite structure and a high density more than 95% of the theoretical density.