Oxide-Ion Conductivity of BaLaInMO_5.5 (M=Sc, Ga and In) and BaLaIn_2-xSc_xO_5.5 (x=0.1, 0.2 and 0.3)

Abstract

Solid solutions of BaLaIn₂O_5.5 and BaLaInMO_5.5 that formed by partial replacement of In by Sc and Ga have a cubic perovskite structure. The Sc³⁺- and Ga³⁺-doped compounds, which had almost the same electrical conductivities, exhibited lower conductivities than the parent compound BaLaIn₂O_5.5 in the temperature range from 573 to 1273K. The Ga compound showed a transference number, t_i, of unity at both high and low oxygen partial pressures in the temperature range from 973 to 1273K. As for the Sc compound kept at 973-1273K, a t_i of nearly unity was observed at low oxygen partial pressure, while the t_i was slightly lower than unity at high oxygen partial pressures at higher temperatures. The In compound had a t_i of almost unity at high oxygen partial pressure, whereas the number decreased to a value less than 0.9 at low partial pressures of oxygen. The stepwise increase in the Sc content from 0.1 to 1.0 in BaLaIn_2-xSc_xO_5.5 caused a monotonic decrease in conductivity. The decrease in conductivity and the increase in activation energy caused by Sc³⁺ and Ga³⁺ doping were ascribed to the partial ordering of originally disordered oxygen vacancies and a decrease in the size of the triangle formed by two A-site cations and one B-site cation, through which the oxide ion proceeds, respectively.