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 (Bi 1/2 Na 1/2 )TiO 3 – y (Bi 1/2 K 1/2 )TiO 3 – z BaTiO 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 (Bi 1/2 Na 1/2 )TiO 3 (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.