Phase Transition Temperatures and Piezoelectric Properties of (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3–BaTiO3 Lead-Free Piezoelectric Ceramics

Abstract

The phase transition temperatures of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2K_1/2)TiO₃–zBaTiO₃) [x+y+z=1, y:z=2:1] [abbreviate to BNBK2:1(x)] ceramics were investigated using electrical measurements. We discussed the determination of the depolarization temperature, T_d, and defined the T_d for (Bi_1/2Na_1/2)TiO₃ (BNT)-based solid solutions. We also determined the rhombohedral–tetragonal phase transition temperatures, T_R–T, for BNBK2:1(x), and verified them using dielectric and piezoelectric measurements. It was demonstrated that T_R–T corresponded with T_d at x=0.94. The existence of an intermediate phase with ferroelectric and antiferroelectric properties at temperatures higher than the T_d around the morphotropic phase boundary (MPB) was also revealed.