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 (XANE S) spectra at the silicon K-edge were recorded. The presence of noble metal s, although their concentration does not exceed 2%, significantly modifies the Si K-edge spectrum. A shoulder on the high-energy side of the white lin e disappears when noble metals are present in the glassy matrix. Analysis o f the noble metal free spectrum was performed by combining molecular dynami cs simulations and multiple scattering calculations, The use of both formal isms allows the determination of the atomic environment up to 4.5 Angstrom around silicon atoms. Multiple scattering calculations permit an elucidatio n of the origin of this peculiar XANES feature, which is a relevant signatu re of the intermediate range structure. The structural changes within the b orosilicate network caused by the incorporation of noble metals are interpr eted in terms of modification of the B-[3]/B-[4] ratio and of the distribut ion of alkali and alkaline-earth ions within the glassy network. (C) 2001 E lsevier Science B.V. All rights reserved.