(Bi_1/2Na_1/2)TiO₃-BaTiO₃ System for Lead-Free Piezoelectric Ceramics

One of the (Bi 1/2 Na 1/2 )TiO 3 (BNT)-based solid solutions, Ba-modified bismuth sodium titanate, (Bi 1/2 Na 1/2 ) 1- x Ba x TiO 3 (BNBT), is studied for its dielectric and piezoelectric properties as a new group of lead-free piezoelectric ceramics. A rhombohedral (F α )-tetragonal (F β ) morphotropic phase boundary (MPB) is shown to exist at x =0.06∼0.07 by X-ray data, and dielectric and piezoelectric properties. BNBT ceramics with the MPB composition are superior as piezoelectric ceramics in high-frequency ultrasonic applications or as piezoelectric actuator materials because of a lower free permittivity, ε 33 T /ε 0 , and a high electromechanical coupling factor, k t or k 33 , along with high mechanical strength.