Valence State of Iron in the Sr₂Fe(Mo,W,Ta)O_6.0 Double-Perovskite System: An Fe K-edge and L_2,3-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, Sr₂FeMoO_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 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 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 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_2,3-edge XANES spectra intermediate spectral features are revealed for the Sr₂FeMoO_6.0 sample in comparison with those for samples heavily substituted with either W or Ta.