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Title: Local electronic structure analysis for brownmillerite Ca(Sr)FeO2.5 using site-resolved energy-loss near-edge structures
Authors: Haruta, M.  kyouindb  KAKEN_id  orcid (unconfirmed)
Kurata, H.  kyouindb  KAKEN_id  orcid (unconfirmed)
Matsumoto, K.
Inoue, S.
Shimakawa, Y.  kyouindb  KAKEN_id  orcid (unconfirmed)
Isoda, S.  kyouindb  KAKEN_id
Author's alias: 治田, 充貴
Keywords: band structure
bonds (chemical)
calcium compounds
charge exchange
crystal field interactions
electron energy loss spectra
electron probe analysis
scanning-transmission electron microscopy
strontium compounds
Issue Date: Aug-2011
Publisher: American Institute of Physics
Journal title: Journal of Applied Physics
Volume: 110
Issue: 3
Thesis number: 033708
Abstract: Oxygen K-edge and Fe L2,3-edge electron energy-loss near-edge structures (ELNES) were measured for FeO6 octahedra and FeO4 tetrahedra in the brownmillerite Ca(Sr)FeO2.5 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 FeO6 octahedra and FeO4 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 FeO6 octahedral site. Additionally, for the oxygen linking the octahedral and tetrahedral Fe sites in CaFeO2.5, charge transfer was found to preferentially occur toward the tetrahedral Fe ions. In the case of SrFeO2.5, 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 FeO6 octahedra in Ca(Sr)FeO2.5, as exhibited by an extension along the b-axis.
Rights: © 2011 American Institute of Physics
DOI(Published Version): 10.1063/1.3610526
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