Oxygen Ion Transport and Effects of Doping in Ba3Ti3O6(BO3)2

Abstract

We report for the first time a combined experimental and computational study of oxygen ion transport and the effects of doping in Ba3Ti3O6(BO3)2, a promising oxyborate for solid-oxide fuel cell applications. Undoped and doped samples were prepared by solid-state reaction and characterized using X-ray diffraction and electrochemical impedance spectroscopy. We find that the undoped sample already has a conductivity level that is quite high, about 1.46 × 10–4 S cm–1 at 700 °C in air. Partial replacement of Ba2+ or Ti4+ by subvalent elements, Ba3–xAxTi3O6(BO3)2 (A = Na+, K+) and Ba3Ti3–xMxO6 (BO3)2 (M = Mg2+, In3+, Sb3+), leads to reduced conductivity, whereas partial replacement of Ti4+ by supervalent elements, Ba3Ti3–xMxO6(BO3)2 (M = Nb5+, Ta5+), increases the conductivity. The measured activation energy is in the range 0.99–1.09 eV for the doped samples (compared to 1.02 eV of the undoped one). The transport properties can be understood in terms of the presence of oxygen and barium vacancies in high concen...