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

Abstract

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 ofmore » 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.« less

Authors:
; ; ; ; ;  [1]
  1. Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan)
Publication Date:
OSTI Identifier:
22036676
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 110; Journal Issue: 3; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 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

Citation Formats

Haruta, M., Kurata, H., Matsumoto, K., Inoue, S., Shimakawa, Y., and Isoda, S. Local electronic structure analysis for brownmillerite Ca(Sr)FeO{sub 2.5} using site-resolved energy-loss near-edge structures. United States: N. p., 2011. Web. doi:10.1063/1.3610526.
Haruta, M., Kurata, H., Matsumoto, K., Inoue, S., Shimakawa, Y., & Isoda, S. Local electronic structure analysis for brownmillerite Ca(Sr)FeO{sub 2.5} using site-resolved energy-loss near-edge structures. United States. doi:10.1063/1.3610526.
Haruta, M., Kurata, H., Matsumoto, K., Inoue, S., Shimakawa, Y., and Isoda, S. Mon . "Local electronic structure analysis for brownmillerite Ca(Sr)FeO{sub 2.5} using site-resolved energy-loss near-edge structures". United States. doi:10.1063/1.3610526.
@article{osti_22036676,
title = {Local electronic structure analysis for brownmillerite Ca(Sr)FeO{sub 2.5} using site-resolved energy-loss near-edge structures},
author = {Haruta, M. and Kurata, H. and Matsumoto, K. and Inoue, S. and Shimakawa, Y. and Isoda, S.},
abstractNote = {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.},
doi = {10.1063/1.3610526},
journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 3,
volume = 110,
place = {United States},
year = {2011},
month = {8}
}