Fe coordination environment in Fe(II)- and Fe(III)-silicate glasses via the Fourier-transform analysis of Fe K-XANES

The Fe-O distances (R1) and the number of nearest oxygen atoms (N1), which coordinate Fe in Fe(II) and Fe(III) containing silicate glasses are determined by the method based on the Fourier-transform analysis of XANES performed for the short k-range and the subsequent fit of the extracted first shell's contribution. The scattering amplitudes for Fe-O pair, used for the fit, are calculated by the HF MT-potential with the neutral electronic configurations of atoms. The validity of this model for the different redox states of Fe in glasses and the accuracy of the determined (R1) and (N1) are analyzed applying the method to the Fe K-XANES of the references – Fe(II) and Fe(III) aqueous sulfate solutions. The modeling of the contribution of the Fe nearest oxygens to the Fe KXANES of Fe(II)- and Fe(III)-rich silicate glasses, as well as in the series of glasses with the mixture of Fe(II) and Fe(III) states, performed through a single-shell fit and a subsequent two-shell fit, provides structural parameters for the oxygen-polyhedron around the ionized Fe2+ and Fe3+ atoms and gives access to the estimates for the Fe2+/Fe3+ ratio changes among all samples studied.