title: An X-ray absorption spectroscopic study on mixed conductive La0.6Sr0.4Co0.8Fe0.2O(3-δ) cathodes. I. Electrical conductivity and electronic structure.
abstract: The electrical conduction mechanism of mixed conductive perovskite oxides, La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ), for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) was annealed under various oxygen partial pressures p(O(2))s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) depended on the annealing p(O(2)), with more oxygen vacancies introduced at lower than at higher p(O(2))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 L(III)-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 La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) decreased with decreasing p(O(2)), due to a decreasing hole concentration.
authors.affiliation: Office of Society-Academia Collaboration for Innovation, Kyoto University, Yoshida-nihonmatsu-cho, Kyoto, Japan. orikasa@h01.mbox.media.kyoto-u.ac.jp
authors.forename: Yuki
authors.initials: Y
authors.lastname: Orikasa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Ina
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nakao
authors.forename: Atsushi
authors.initials: A
authors.lastname: Mineshige
authors.forename: Koji
authors.initials: K
authors.lastname: Amezawa
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Oishi
authors.forename: Hajime
authors.initials: H
authors.lastname: Arai
authors.forename: Zempachi
authors.initials: Z
authors.lastname: Ogumi
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Uchimoto