The electrical conduction mechanism of mixed conductive perovskite oxides, La0.6Sr0.4Co0.8Fe0.2O 3-δ, for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La0.6Sr0.4Co0.8Fe0.2O 3-δ was annealed under various oxygen partial pressures p(O2)s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La0.6Sr0.4Co 0.8Fe0.2O3-δ depended on the annealing p(O2), with more oxygen vacancies introduced at lower than at higher p(O2)s. X-Ray absorption spectroscopic measurements were performed at the O K-, Co L-, Fe L-, Co K-, and Fe K-edges. The valence states of the Co and Fe ions were investigated by the X-ray absorption near edge structure (XANES) at the Co and Fe LIII-edges. While the Fe average valence was almost constant, the valence of the Co ions decreased with oxygen vacancy introduction. The O K-edge XANES spectra indicated that electrons were injected into the Co 3d/O 2p hybridization state with oxygen vacancy introduction. Both absorption edges at the Co and Fe K-edge XANES shifted towards lower energies with oxygen vacancy introduction. The shift at the Co K-edge resulted from the decrease in the Co average valence and that at the Fe K-edge appeared to be caused by changes in the coordination environment around the Fe ions. The total conductivity of La0.6Sr0.4Co0.8Fe 0.2O3-δ decreased with decreasing p(O2), due to a decreasing hole concentration.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry