Valence state of iron in, the Sr2Fe(Mo,W,Ta)O6.0 double-perovskite system:: an FeK-edge and L2,3-edge XANES study

Here we employ both Fe K and L-2,L-3 edge X-ray absorption near-edge structure (XANES) spectroscopy techniques to clarify that in the B-site ordered double-perovskite halfmetal, Sr2FeMoO6.0, 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 Sr2Fe(Mo,W/Ta)O-6.0 system. Replacing Mo-V/VI gradually with W-VI causes an increasing amount of Fe to adopt the FeII 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 Sr2Fe(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,L-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.