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

TL;DR

This study uses Fe K and L2,3-edge XANES spectroscopy to determine the mixed-valence states of iron and molybdenum in Sr2Fe(Mo,W,Ta)O6.0 double-perovskites, revealing how elemental substitution affects their valence states.

Contribution

It provides a detailed spectroscopic analysis of valence states in Sr2Fe(Mo,W,Ta)O6.0, clarifying the effects of W and Ta substitutions on iron and molybdenum valences.

Findings

Iron exhibits a mixed FeII/III valence in Sr2FeMoO6.0.

Substituting WVI increases FeII content, while TaV shifts Fe towards FeIII.

Absorption energy shifts correlate with iron valence changes.

Abstract

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.