Electrical Properties and Depolarization Temperature of (Bi 1/2 Na 1/2 )TiO 3 –(Bi 1/2 K 1/2 )TiO 3 Lead-free Piezoelectric Ceramics

The piezoelectric properties of a solid solution of the binary system, x (Bi 1/2 Na 1/2 )TiO 3 –(1- x )(Bi 1/2 K 1/2 )TiO 3 [BNKT100 x ; x =0.50–0.98] were investigated, focusing on depolarization temperature, T d . Fine piezoelectric properties in lead-free piezoelectric ceramics were obtained near the morphotropic phase boundary (MPB) composition between the rhombohedral and tetragonal structures, and the highest electromechanical coupling factor, k 33 , and piezoelectric constant, d 33 , were 0.56 for BNKT84 and 157 pC/N for BNKT80, respectively. However, the T d of BNKT80 was low (174 °C). The T d of the MPB composition was low, and the T d near the MPB composition was sharply decreased. It is thought that BNKT70 is a candidate composition for lead-free actuator applications owing to its relatively large piezoelectric constant, d 33 (126 pC/N), dynamic d 33 (214 pm/V), and high depolarization temperature, T d (206 °C). In this study, we determined depolarization temperature, T d , from the temperature dependence of dielectric and piezoelectric properties.