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The valence state of iron in the Sr2Fe(Mo,W,Ta)O6.0 double-perovskite system An Fe K-edge a.pdf

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The valence state of iron in the Sr2Fe(Mo,W,Ta)O6.0 double-perovskite system An Fe K-edge a

Chemistry of Materials Accepted for publication The valence state of iron in the Sr2Fe(Mo,W,Ta)O6.0 double-perovskite system: An Fe K-edge and L2,3-edge XANES study M. Karppinen,1* H. Yamauchi,1 Y. Yasukawa,1 J. Lindén,2 T. S. Chan,3 R. S. Liu,3 and J. M. Chen4 1Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan 2Physics Department, ?bo Akademi, FIN-20500 Turku, Finland 3Department of Chemistry, National Taiwan University, Taipei, Taiwan, Republic of China 4National Synchrotron Radiation Research Center, Hsinchu, Taiwan, Republic of China *Corresponding author (e-mail: karppinen@msl.titech.ac.jp) Here we employ both Fe K and L2,3 edge x-ray absorption near-edge structure (XANES) spectroscopy techniques to clarify that iron in the B-site ordered double-perovskite halfmetal, Sr2FeMoO6.0, possesses a mixed-valence state, FeII/III, and accordingly molybdenum a mixed MoV/VI valence state. A reliable interpretation of the spectral features has been made possible by using a series of samples of the Sr2Fe(Mo,W/Ta)O6.0 system. Replacing MoV/VI gradually with WVI causes increasing amount of Fe to adopt the FeII state, whereas TaV substitution shifts the valence of iron towards FeIII. As the valence of Fe increases from II to III in the Sr2Fe(Mo,W/Ta)O6.0 system, the absorption energy at the Fe K-edge gradually shifts towards the higher energy side. Similarly, in the L2,3-edge XANES spectra intermediate spectral features are revealed for the Sr2FeMoO6.0 sample in comparison with those for samples heavily substituted with either W or Ta. Keywords: Fe valence, XANES spectroscopy, Double perovskite, Halfmetal Introduction The B-site ordered double perovskites, A2BB’O6-w, are derived from the simple perovskite compounds, ABO3, upon co-occupation of the octahedral cation site with two different metal species of different charges. Such category of compounds has been re-highlighted since room