Thermodynamic modelling of the real-space correlation function for four sodium borosilicate glasses

The interpretation of even the first peak in the total correlation function, T(r), for a multicomponent oxide glass is extremely complex, especially when the glass contains more than one glassforming oxide and hence a number of different structural unit species. In the case of alkali borosilicate glasses, there are five possible borate and five possible silicate structural unit species, all of which have slightly different bond lengths and internal angles. In addition, these bond lengths and angles vary in a systemmatic way when the basic borate structural units are incorporated into superstructural units. In the present paper, the model of associated solutions is used to predict the detailed shape of the first two peaks in T(r) for four sodium borosilicate glasses with nominal Na2O:B2O3:SiO2 ratios of 2:2:1, 1:1:1, 1:1:6 and 1:1:8. It is concluded that the agreement between the thermodynamic model and experiment is within their combined uncertainty. The main limitation at present is lack of knowledge concerning the structure of relevant crystalline phases, especially their high temperature polymorphs.