High-field electromechanical response of Bi0.5Na0.5TiO3?Bi0.5K0.5TiO3 across its morphotropic phase boundary

Lead-free (1 − x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3 [(BNKTx); x = 0.18, 0.20, 0.22, 0.24] piezoelectric ceramics were prepared via conventional solid-state reactions. Phase characterization using x-ray diffraction showed coexistence of perovskite rhombohedral and tetragonal polymorphs as anticipated for compositions across the morphotropic phase boundary (MPB). Electrical and electromechanical properties were studied as a function of x. Permittivity and polarization figures were comparable to the best values previously reported. Largest piezoelectric and high field electromechanical responses were obtained for BNKT0.20 samples, considered to have optimum MPB phases. This material exhibited giant field-induced strains of 0.13% and 0.38% under electric fields of 1 and 2.4 kV mm−1 at room temperature by a phase-change mechanism. Figures are comparable to those reported for other BNT-based systems, but under significantly lower driving fields, which is a clear advantage for actuation.