Molecular dynamics simulation of sodium borosilicate glasses

Abstract

Molecular dynamics (MD) calculations of (B 2O 3) x (Na 2Si 2O 5) (1− x) glasses have been performed using Born–Mayer–Huggins interatomic potentials together with three-body potentials and increasing B 2O 3 concentrations examined ( x=0.3, 0.5 and 0.7). The main features in the total radial distribution functions (RDFs) are directly attributable to those found empirically in B 2O 3 and Na 2Si 2O 5 glasses. Simulations confirm that there is also a tendency for the borate component of the network to separate from the silicate part and for sodium to associate with the former. As the B 2O 3 content, x, rises the Na 2O/B 2O 3 ratio, R, falls and the fraction of compensated tetrahedral boron sites shifts in favour of 3-fold co-ordinated borons. Indeed, as x increases, the co-ordination of sodium also increases, reflecting its higher co-ordination in borate than in silicate glasses. Compared to binary borate glasses, these changes in the short range order of (B 2O 3) x (Na 2Si 2O 5) (1− x) glasses are extended because of the widely ranging SiO 2/B 2O 3 ratio, K.