Phase transition, ferroelectric and piezoelectric properties of B-site complex cations (Fe0.5Nb0.5)4+-modified Ba0.70Ca0.30TiO3 ceramics

Abstract Ba0.70Ca0.30Ti1-x (Nb0.5Fe0.5)xO3 lead-free ceramics (abbreviated as BCTNFx, x = 0–0.12) were prepared by solid-state reaction method. The influence of B-site (Fe0.5Nb0.5)4+ substitution on phase structure, microstructure, dielectric, ferroelectric and piezoelectric properties of Ba0.70Ca0.30TiO3 ceramics were systematically studied. The BCTNFx ceramics consist of diphasic tetragonal (T) and orthorhombic (O) phases at x = 0–0.04, pseudocubic (PC) and O phases at x = 0.05–0.08, cubic (C) and O phases at 0.08  e r  = 1268, tan δ  = 0.03, Tm = 102 °C, Pmax = 12.8 μC/cm2, Pr = 6.1 μC/cm2, EC = 6.0 kV/cm, d33 = 117 pC/N, kp% = 0.18%, Qm = 236, bipolar Smax% = 0.20%, unipolar Smax% = 0.16% and d 33 ∗  = 314 pm/V. The variation of electrical properties of BCTNFx ceramics is attributed to the combined action of grain size effect, phase transition, weakness of octahedral distortion, clamping effects of the internal bias electric field Ei on domain wall motion induced by B-site cations (Fe0.5Nb0.5)4+ displacement.