Destabilization of ferroelectric order in bismuth perovskite ceramics by A-site vacancies

This work compared the effects of isovalent Sn4+ and aliovalent Ta5+ doping on Ti-sites in lead-free perovskite type Bi1/2(Na0.82K0.18)1/2TiO3 piezoelectric ceramics on their ferroelectric and electric field-induced strain behavior. Both impurities led to a diffuse transformation from the coexistence of ferroelectric rhombohedral and tetragonal phases to a nonpolar pseudocubic symmetry. Nevertheless, Ta doping more strongly promoted the phase transition even though the ionic size difference between Ta5+ and Ti4+ was smaller than that between Sn4+ and Ti4+. The results evidenced that donor-induced A-site vacancies significantly contributed to the destabilization of ferroelectric phases in the Bi perovskite. ► We compared donor and isovalent ion doping into Bi-based lead-free ceramics. ► The ferroelectric order becomes disrupted when the tolerance factor decreases. ► A-site vacancies contribute to the destabilization of the ferroelectric order.