The effect of redox state on the local structural environment of iron in silicate glasses: a combined XAFS spectroscopy, molecular dynamics, and bond valence study

Abstract : A series of 27 silicate glasses of various compositions containing 0.2–2 at.% iron were synthesized at various oxygen fugacity values. The glasses were examined using X-ray absorption fine structure (XANES) spectroscopy at the Fe K-edge in order to determine iron oxidation state and first-neighbor coordination number. Spectral information extracted from the pre-edge region and principal component analysis (PCA) of the XANES region, together with a spectral inversion, were used to derive the end-member spectral components for Fe(II) and Fe(III). Linear trends in the pre-edge features were observed for most compositional series of the glasses examined as a function of Fe(II)/Fe(III) content. These linear trends are believed to be due to the similarity of average coordination numbers for both Fe(II) and Fe(III) end-members in each series. This result is consistent with model simulations of the XANES region and molecular dynamics (MD) simulations for the two end-member compositions which also show that Fe(II) and Fe(III) have similar average coordination numbers. These simulations also suggest the presence of five-coordinated Fe(III) in the melt phase. Based on a bond valence analysis of these MD simulations, a simple model is proposed to help predict the speciation of iron in oxide and silicate glasses and melts.
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François Farges, Yannick Lefrère, Stéphanie Rossano, Anne Berthereau, Georges Calas, et al.. The effect of redox state on the local structural environment of iron in silicate glasses: a combined XAFS spectroscopy, molecular dynamics, and bond valence study. Journal of Non-Crystalline Solids, Elsevier, 2004, 344, pp.176-188. ⟨10.1016/j.jnoncrysol.2004.07.050⟩. ⟨hal-00085025⟩

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