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

Here we employ both Fe K and L 2,3 edge X-ray absorption near-edge structure (XANES) spectroscopy techniques to clarify that in the B -site ordered double-perovskite halfmetal, Sr 2 FeMoO 6.0, iron possesses a mixed-valence state, Fe II/III, and accordingly, molybdenum a mixed Mo V/VI valence state. A reliable interpretation of the spectral features has been made possible by using a series of samples of the Sr 2 Fe(Mo,W/Ta)O 6.0 system. Replacing Mo V/VI gradually with W VI causes an increasing amount of Fe to adopt the Fe II state, whereas Ta V substitution shifts the valence of iron toward Fe III . As the valence of Fe increases from II to III in the Sr 2 Fe(Mo,W/Ta)O 6.0 system, the absorption energy at the Fe K -edge gradually shifts toward the higher energy side. Similarly, in the L 2,3 -edge XANES spectra intermediate spectral features are revealed for the Sr 2 FeMoO 6.0 sample in comparison with those for samples heavily substituted with either W or Ta.