A thermodynamic, molecular dynamics and neutron diffraction investigation of the distribution of tetrahedral {;Si(n)} species and the network modifying cation environment in alkali silicate glasses

Abstract

Previous molecular dynamics (MD) simulations of alkali silicate glasses are extended to keep a separate record of the bridging and non-bridging oxygen atoms and the SiO and NaO first neighbour distance distributions are compared with those extracted from neutron diffraction data. The model of ideal associated solutions is used to predict the distributions of Si(n) tetrahedral species for the glasses studied and these are in good agreement with nuclear magnetic resonance data. However, the corresponding distributions for the MD simulations indicate a much higher fictive temperature than for the real glasses. The spatial distribution of the Si(4) species for the MD simulations is more uniform than would pertain if the various Si(n) species were interconnected randomly, which has implications for the modified random network theory.