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

Laboratoire de Minéralogie-Cristallographie, UMR CNRS 7590, Universités Paris 6 et 7, IPGP, Tour 16, case 115, 4 place Jussieu, F-75252 Paris cedex 05 France; Comissariat à l'Energie Atomique, DCC/DRRV/SCD, Marcoule, BP 171, F-30207 Bagnols/Cèze, France; Laboratório Nacional de Luz Sı̀ncrotron, CP 6192, 13083-970 Campinas, São Paulo, Brazil; LURE, Centre Universitaire Paris-Sud, Bâtiment 209D, BP34, F-91898 Orsay cedex, France; Laboratoire des géomatériaux, Université de Marne-la-vallée, 5 Bd Descartes, Champs/Marne, F-77454 Marne-la-Vallée cedex 2, France
Journal of Non-Crystalline Solids (Impact Factor: 1.72). 08/2001; DOI: 10.1016/S0022-3093(01)00733-5

ABSTRACT 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The Mo environment has been investigated in inactive nuclear glasses using extended X-ray absorption spectroscopy (XAS). Mo is present in a tetrahedron coordinated to oxygen in the form of molybdate groups [MoO4]2− (d(Mo–O)=1.78 Å). This surrounding is not affected by the presence of noble metal phases in the nuclear glass. Relying on the XAS results, on the bond-valence model and on molecular dynamics simulations of a simplified borosilicate model glass, we show that these groups are not directly linked to the borosilicate network but rather located within alkali and alkaline-earth rich domains in the glass. This specific location in the glass network is a way to understand the low solubility of Mo in glasses melted under oxidizing conditions. It also explains the possible phase separation of a yellow phase enriched in alkali molybdates in molten nuclear glasses or the nucleation of calcium molybdates during thermal aging of these glasses. Boron coordination changes in the molten and the glassy states may explain the difference in the composition of the crystalline molybdates, as they exert a direct influence on the activity of alkalis in borosilicate glasses and melts.
    Journal of Nuclear Materials 10/2003; 322(1):15-20. · 2.02 Impact Factor
  • Source
    Zeitschrift fur Kristallographie. 07/2012; 227(7):494-504.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Si K-edge X-ray absorption near edge structure (XANES) spectra were collected from Ti-bearing alkali and alkaline-earth silicate glasses with metasilicate (R2O/SiO2) compositions where R=Na2O, K2O and CaO. The Si K-edges of the Na2SiO3, K2SiO3, and CaSiO3 glasses containing TiO2 are observed at ∼0.8, ∼0.9, and ∼1.0 eV lower energy than that of silica glass (a-SiO2), respectively, and shift to higher energy with added TiO2. This indicates that the glasses are less polymerised than a-SiO2 but become more polymerised with increasing TiO2. Ti is predominantly acting as a network former and this is reflected at the local Si environment as an increase in polymerisation. A broad resonance near ∼1864 eV is related to the average Si–O–Si angle and/or the Si–O bond strength. In addition, a resonance observed at ∼2–5 eV above the absorption edge is located at a similar energy to one assigned to [6]Si in silicophosphate glasses and may interfere with resonance area calculations used to quantify [6]Si in those glasses. The presence of this resonance indicates changes in the median range structure; in particular, changes in the oxygen environment surrounding the Si atoms.
    Chemical Geology 12/2004; 213(s 1–3):31–40. · 3.48 Impact Factor

Full-text (2 Sources)

Available from
May 31, 2014