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 behaviour. 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.

Destabilization of Ferroelectric Order in Bismuth Perovskite Ceramics by A-Site Vacancies. H.S.Han, C.W.Ahn, I.W.Kim, A.Hussain, J.S.Lee: Materials Letters, 2012, 70, 98–100