Ordered and disordered models of local structure around Ag cations in silver borate glasses based on x-ray absorption near-edge structure spectroscopy

The local coordination of Ag cations in silver borate glasses ${\mathrm{Ag}}_2\mathrm{O}\cdot \mathrm{n}{\mathrm{B}}_2{\mathrm{O}}_3$ has been studied by comparing the experimental x-ray absorption near edge structure (XANES) at the Ag K edge with results of theoretical simulations. We demonstrate that simple models which describe the local structure around Ag with a single geometric configuration cannot be reconciled with experimental XANES spectra. In order to obtain a satisfactory agreement between theory and experiment, it is necessary to include the disorder also at the short range. Structural information is extracted from XANES data using an empirical approach, which is based on the presence of a multiplicity of atomic structural configurations around photoabsorbing atoms. This approach is particularly suited for describing the local environment of atomic species belonging to glass network modifiers.