Medium range structure of borosilicate glasses from Si K-edge XANES: a combined approach based on multiple scattering and molecular dynamics calculations.

In order to better understand the influence of noble metals precipitated in a borosilicate glass structure, X-ray absorption near-edge structure (XANES) spectra at the silicon K-edge were recorded. The presence of noble metals, although their concentration does not exceed 2%, significantly modifies the Si K-edge spectrum. A shoulder on the high-energy side of the white line disappears when noble metals are present in the glassy matrix. Analysis of the noble metal free spectrum was performed by combining molecular dynamics simulations and multiple scattering calculations. The use of both formalisms allows the determination of the atomic environment up to 4.5 Å around silicon atoms. Multiple scattering calculations permit an elucidation of the origin of this peculiar XANES feature, which is a relevant signature of the intermediate range structure. The structural changes within the borosilicate network caused by the incorporation of noble metals are interpreted in terms of modification of the [3]B/[4]B ratio and of the distribution of alkali and alkaline-earth ions within the glassy network