Phase transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3-BaTiO3 lead-free piezoelectric ceramics

The phase transition temperatures of x(Bi1/2Na1/2)TiO3-y(Bi1/2K1/2)TiO3-zBaTiO(3)) [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 (Bi1/2Na1/2)TiO3 (BNT)-based solid solutions. We also determined the rhombohedral-tetragonal phase transition temperatures, TR-T, for BNBK2:1(x), and verified them using dielectric and piezoelectric measurements. It was demonstrated that TR-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.