Molecular dynamics simulation of sodium borosilicate glasses

Molecular dynamics (MD) calculations of (B2O3)x(Na2Si2O5)(1−x) glasses have been performed using Born–Mayer–Huggins interatomic potentials together with three-body potentials and increasing B2O3 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 B2O3 and Na2Si2O5 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 B2O3 content, x, rises the Na2O/B2O3 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 (B2O3)x(Na2Si2O5)(1−x) glasses are extended because of the widely ranging SiO2/B2O3 ratio, K.