Suppression of electrical conductivity and switching of conduction mechanisms in ‘stoichiometric’ (Na0.5Bi0.5TiO3)1−x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions

Abstract

(Na_0.5Bi_0.5TiO₃)_1−x(BiAlO₃)_x (0 ≤ x ≤ 0.08) solid solutions were prepared by a solid state reaction and their electrical properties were established by ac impedance spectroscopy and electromotive force transport number measurements. Incorporation of BiAlO₃ (BA) decreases the electrical conductivity of Na_0.5Bi_0.5TiO₃ (NBT) and sequentially changes the conduction mechanism with increasing x from predominant oxide-ion conduction to mixed ionic–electronic conduction and finally to predominant electronic conduction. The suppressed oxide-ion conduction by BA incorporation significantly reduces the dielectric loss at elevated temperatures and produces excellent high-temperature dielectric materials for high BA contents. The possible reasons for the suppressed oxide-ion conduction in the NBT–BA solid solutions have been discussed and we propose that the local structure, especially trapping of oxygen vacancies by Al³⁺ on the B-site, plays a key role in oxide-ion conduction in these apparently ‘stoichiometric’ NBT-based solid-solution perovskite materials.