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

(1−x)(Bi0.5Na0.5)TiO3–xBaTiO3 ceramics (x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 0.90) were fabricated by a conventional solid-state reaction and their phase transitions and piezoelectric properties were investigated using XRD analyses, Curie temperature, the frequency dependance of dielectric constant, and P–E curves. A complete solid solution with a perovskite structure was formed in the whole composition range of BNT–BT and more than two phase transitions arising from a compositional change were found. With increasing BaTiO3 content, the sequence of phase transitions from a rhombohedral structure to unknown tetragonal structures and finally a tetragonal structure with the space group P4mm has been established. While the rhombohedral–tetragonal phase transition led to superior piezoelectric properties in BNT–BT ceramics, other phase transitions between tetragonal structures had a little effect on piezoelectric properties. The d33, εr, kp, kt, and Qm and values lied in ranges of 40–130 pC/N, 400–900, 10–30%, 15–30%, and 50–250, respectively.