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Original article (peer-reviewed)

Journal Chem. Mater.
Volume (Issue) 24(8)
Page(s) 1529 - 1535
Title of proceedings Chem. Mater.
DOI 10.1021/cm300423m

Abstract

Iron perovskites of the ABO3 type with stoichiometry La1/2Sr1/2Fe(1-x)MexO3-δ have been substituted with 10% Ta and 20% Ti %, and heat treated in air or in argon. 10% substitution of iron by tantalum in the hole-doped La1/2Sr1/2FeO3 decreases the electric conductivity by around three orders of magnitude. The conductivity decrease is well correlated with a decrease of the isothermal lattice expansion, a decrease of the formal and actual Fe4+/Fe3+ ratio, and with a shift of the spectral weight within the O(2p)-Fe(3d) mixed states from levels with eg symmetry near the Fermi energy to levels with t2g symmetry. Systematic and corresponding differences in the Fe (2p) and O (1s) X-ray absorption spectra reveal that the preparation in an oxygen-rich atmosphere promotes the formation of states with increased covalence in the initial state and states which contain O (2p) character. The electron hole doping peak in the oxygen pre-edge NEXAFS spectra is virtually absent when the samples were heated in argon. The corresponding Fe core level spectra show no significant differences other than in the branching ratio of L2 and L3 peaks, suggesting that the (3d) states are localized, and that hole states are responsible for electric transport changes in the material.
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