Unravelling the La dopant induced physicochemical changes and the electrical behaviour on BaFeO3 under oxidising and reducing atmospheres

Abstract

Electroceramic oxides like La-doped BaFeO3 garner greater interest owing to their tunability of mixed ionic conduction. However, reports on the effect of La on the microstructural changes, the type of conduction mechanism under different atmospheres and the negative charge transfer influenced by the Fe-O hybridization in Ba1−xLaxFeO3−δ are hardly available. Doping La induces cation vacancies and Fe reduction, creating nanorod decorated surface after the high-temperature treatment. Conductivity studies expose the rate-limiting steps for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) as the ohmic resistances and Ba segregation effects. Among the samples studied, Ba0.9La0.1FeO3−δ performs better at 800 °C with an activation energy of ∼0.35 eV under both oxidizing and reducing atmospheres. Surface analysis after EIS reveals Fe and O with different oxidation states that enhance the total conductivity. The amount of hydroxyl species retained (23.66% for Ba0.9La0.1FeO3−δ ) and the ratio of the adsorbed to the lattice oxygen (15.33% for Ba0.9La0.1FeO3−δ ) gives insight on HOR and ORR activities. Also, computational studies validated the negative charge transfer mechanism of the samples under thermally assisted oxidation. The results indicate Ba0.9La0.1FeO3−δ as a tuneable electrode for solid oxide cells.