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

(Na0.5Bi0.5TiO3)1-x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions were prepared by solid state reaction and their electrical properties established by ac impedance spectroscopy and electromotive force transport number measurements. Incorporation of BiAlO3 (BA) decreases the electrical conductivity of Na0.5Bi0.5TiO3 (NBT) and with increasing x sequentially changes the conduction mechanism 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. Possible reasons for the suppressed oxide-ion conduction in the NBT-BA solid solutions are discussed and we propose the local structure, especially trapping of the oxygen vacancies by Al3+ on the B-site, plays a key role in the oxide-ion conduction in these apparently ‘stoichiometric’ NBT-based solid-solution perovskite materials.