Investigation of multicomponent silicate glasses by coupling WAXS and molecular dynamics.
Résumé
An innovative method coupling molecular dynamics (MD) and reverse Monte Carlo (RMC) analysis allowed us to fit the interaction potentials on the experimental structure factors of aluminoborosilicate glass compositions obtained by wide-angle X-ray diffraction spectrometry (WAXS). By calculating the structural factors and the partial radial distribution functions, the combination of RMC and MD directly identifies the pair potentials requiring optimization. We observed that a Coulomb potential alone is not enough to model a sufficiently ordered local environment around the Na and Ca cations: additional terms were necessary to fit the repulsion and attraction terms. Analysis of the glass atomic structure revealed a larger number of F1–O–F2 groups in the glass containing CaO (where Fi=Al or B ions), although the total number of these groups remains lower than would be expected from a random ion distribution. The relatively higher Ca coordination number around Al compared with B ions shows a preferential Ca–Al approach compared with Ca–B. Finally, analysis of the Na and Ca environments showed that the Na ions more readily act as pure charge compensators – i.e., distant from any non-bridging oxygen atoms – than do the Ca ions, most of which conserve non-bridging oxygen atoms in their local environment.