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International audienceX-ray absorption spectroscopy at the Mg K-edge is used to obtain information on magnesium environment in minerals, silicate and alumino-silicate glasses. First-principles XANES calculations are performed for minerals using a plane-wave density functional formalism with core-hole effects treated in a supercell approach. The good agreement obtained between experimental and theoretical spectra provides useful information to interpret the spectral features. With the help of calculation, the position of the first peak of XANES spectra is related to both coordination and polyhedron distortion changes. In alumino-silicate glasses, magnesium is found to be mainly 5-fold coordinated to oxygen whatever the aluminum saturation index value. In silicate glasses, magnesium coordination increases from 4 in Cs-, Rb- and K-bearing glasses to 5 in Na- and Li-bearing glasses but remains equal as the polymerization degree of the glass varies. The variation of the C feature (position and intensity) is strongly related to the alkali type providing information on the medium range order

Sodium-covered silica films formed on silicon substrates are examined by X-ray photoemission spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (EXAFS) in ultrahigh vacuum conditions. The presence of sodium, which diffuses within the silica matrix at 300 K results in a shift of the O 1s core level toward lower binding energy with respect to the bulk silica close to the energy separation between the O 1s level associated with bridging and nonbridging oxygen in soda−silica glass. The EXAFS at the sodium K edge shows that a defined stereochemichal order, similar to that which is observed in glass, arises in the silica matrix around this element since sodium atoms are surrounded by oxygen atoms at an average distance of 2.3 Å and by a second shell which is assigned to silicon atoms located at 3.8 Å.