Local electronic structure analysis for brownmillerite Ca(Sr)FeO{sub 2.5} using site-resolved energy-loss near-edge structures

Journal Article · Mon Aug 01 04:00:00 EDT 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3610526· OSTI ID:22036676

Haruta, M; Kurata, H; Matsumoto, K; Inoue, S; Shimakawa, Y; Isoda, S ^[1]

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1. Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan)

Oxygen K-edge and Fe L{sub 2,3}-edge electron energy-loss near-edge structures (ELNES) were measured for FeO{sub 6} octahedra and FeO{sub 4} tetrahedra in the brownmillerite Ca(Sr)FeO{sub 2.5} by focusing an electron probe at individual Fe sites using scanning transmission electron microscopy combined with electron energy-loss spectroscopy. The observed site-resolved oxygen K-ELNES showed different features reflecting the local chemical bonding around the FeO{sub 6} octahedra and FeO{sub 4} tetrahedra. A pre-peak in the O K-edge spectra, which is attributed to a transition to an unoccupied O 2p band hybridized with the Fe-3d band, shows splitting in the spectrum of the FeO{sub 6} octahedral site. Additionally, for the oxygen linking the octahedral and tetrahedral Fe sites in CaFeO{sub 2.5}, charge transfer was found to preferentially occur toward the tetrahedral Fe ions. In the case of SrFeO{sub 2.5}, charge transfer from the oxygen located in the ac plane was biased toward the tetrahedral Fe atoms. Based upon an analysis of the pre-peak intensity of the O K-ELNES, it was concluded that bonding between the oxygen and iron atoms at the tetrahedral site was more covalent in character than at the octahedral site. The strong covalent character of the tetrahedral sites would be one of the reasons for distortion in the FeO{sub 6} octahedra in Ca(Sr)FeO{sub 2.5}, as exhibited by an extension along the b-axis.

• OSTI ID: 22036676
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 3 Vol. 110; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CALCIUM COMPOUNDS
CHARGE EXCHANGE
CHEMICAL BONDS
COVALENCE
CRYSTAL FIELD
ELECTRON PROBES
ELECTRONIC STRUCTURE
ELECTRONS
ENERGY-LOSS SPECTROSCOPY
IRON
IRON IONS
IRON OXIDES
OXYGEN
STRONTIUM COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY