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

Previous molecular dynamics (MD) simulations of alkali silicate glasse s are extended to keep a separate record of the bridging and non-bridg ing oxygen atoms and the Si-O and Na-O first neighbour distance distri butions are compared with those extracted from neutron diffraction dat a. The model of ideal associated solutions is used to predict the dist ributions of Si-(n) tetrahedral species for the glasses studied and th ese are in good agreement with nuclear magnetic resonance data. Howeve r, the corresponding distributions for the MD simulations indicate a m uch higher fictive temperature than for the real glasses. The spatial distribution of the Si-(4) species for the MD simulations is more unif orm than would pertain if the various Sit((n)) species were interconne cted randomly, which has implications for the modified random network theory.