(Bi_1/2Na_1/2)TiO₃-(Bi_1/2K_1/2)TiO₃-BaTiO₃-Based Lead-Free Piezoelectric Ceramics

Abstract

The piezoelectric properties of lead-free x (Bi 1/2 Na 1/2 )TiO 3 - y (Bi 1/2 K 1/2 )TiO 3 - z BaTiO 3 [BNBK y : z ( x ); y : z = 4:1 and 2:1, x + y + z =1] with tetragonal compositions were investigated, focusing on the secondary phase transition T 2 from the ferroelectric to antiferroelectric phases. Although the T 2 temperatures of BNBK near the MPB composition remained at about 115°C, T 2 rapidly shifted to a higher temperature of 200°C or higher for the off-MPB composition [ x ≤0.75 for BNBK4:1( x ) and x ≤0.78 for BNBK2:1( x )]. The piezoelectric activities of off-MPB compositions decreased with decreasing the amount ( x ) of BNT. The larger piezoelectric constant d 33 =135 pC/N, the higher secondary phase transition temperature T 2 =197°C, and the coupling factor k 33 =0.45 with a good temperature dependence were obtained for BNBK2:1(0.78).