Experimental and theoretical study of the structural environment of magnesium in minerals and silicate glasses using X-ray absorption near-edge structure |
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| Authors: | Nicolas Trcera Delphine Cabaret Stéphanie Rossano François Farges Anne-Marie Flank Pierre Lagarde |
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| Institution: | (1) Laboratoire Géomatériaux et Géologie de l’Ingénieur (G2I), Université Paris-Est, EA 4119, 5 bd Descartes, 77454 Marne la Vallée Cedex 2, France;(2) IMPMC, UMR7590, Universités Paris 6 et 7, CNRS, IPGP, 140 rue de Lourmel, 75015 Paris, France;(3) Laboratoire de Minéralogie (USM 201), Muséum National d’Histoire Naturelle, CNRS UMR 7160, 61 rue Buffon, 75005 Paris, France;(4) CNRS UR1 Soleil, BP 48, 91192 Gif sur Yvette, France |
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| Abstract: | X-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.
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| Keywords: | Magnesium X-ray absorption spectroscopy XANES Ab initio calculation Minerals Glasses |
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