Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi0.5Na0.5TiO3–y BaTiO3–z Bi0.5K0.5TiO3 piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 − x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d33 = 170 pC/N, kp = 0.35 and kt = 0.53. In the case of (1 − x) BNT–x BKT compositions, the d33, kp and kt are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d33 = 133 pC/N, kp = 0.26 and kt = 0.57).