On the nature of native defects in high OH-content silica glasses: A first-principles studyM. Benoit1, M. Pöhlmann2 and W. Kob3
1 CEMES - 29 rue Jeanne Marvig, BP 94347, 1055 Toulouse Cedex 4, France, EU
2 AREVA NP GmbH - Paul-Gossen-Str. 100, 91058 Erlangen, Germany, EU
3 LCVN, CNRS UMR 5587 and Université Montpellier II - 34095 Montpellier, France, EU
received 9 October 2007; accepted in final form 10 April 2008; published June 2008
published online 26 May 2008
First-principles simulations based on the density functional theory are used in order to generate silica glasses containing 3.84 wt % water molecules employing different quench protocols. Using the Kohn-Sham density of states we find localized states in the band gap that can be associated with doubly occupied Si-O dangling bond (DB) which are negatively charged and are compensated by positively charged threefold coordinated oxygens. The position of these states above the O 2p valence band depends on the local environment of the dangling bonds, in particular on the presence of other defects in their neighborhood, and on the hydrogen bond length. These native defects, which could exist in optical fibers for instance, are compatible with the optical absorption and photoluminescence bands observed in amorphous silica and their dependence in the OH content. If present, these pre-existing defects would play a significant role as precursors in the laser-induced defect formation process.
71.23.-k - Electronic structure of disordered solids.
71.15.Pd - Molecular dynamics calculations (Car-Parrinello) and other numerical simulations.
61.43.Fs - Glasses.
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