XANES studies of Fe-bearing glasses

The information about the local environment and valence ratio Fe3+/Sigma Fe (Sigma Fe=Fe3++Fe2+) of Fe ions in silicate glasses has not yet been compl etely understood. Here we present the results of the experimental X-ray abs orption near edge structure (XANES) at Fe K edge in conjunction with ab ini tio full multiple-scattering (MS) simulations in silicate glasses by using proposed Fe tetrahedral and pentahedral cluster models. Our main results ar e: (1) the coordination number (CN) of Fe ions is mainly fourfold-coordinat ed with probably a small part of fivefold structure; (2) the bond length of Fe-O are 1.90 Angstrom for Fe-[4](III)-rich glass and 2.01 Angstrom for Fe -[4](II)-rich glass, respectively, similar or slightly larger than that of tetrahedrally coordinated Fe states in crystalline materials.