Topological model for Bi2O3-NaPO3 glasses. I. Prediction of glass transition temperature and fragility

Abstract In this report, a topological constraint model is developed to predict the glass transition temperature (Tg) and liquid fragility (m) of xBi2O3·(1-x)NaPO3 glass-forming systems by considering the hierarchy of temperature-dependent constraints, including contributions from the modifying cations (Bi3+ and Na+). The model is shown to give an accurate prediction of the Tg and m as a function of composition (x). The increase of Tg with x is mainly caused by the formation of the Bi O linear constraints and also contributions from O–Bi–O angular constraints, which increase the connectivity of the network. The model also accurately predicts the trend of m with composition, which shows a minimum at around x = 5 mol% due to the competition between the contributions from the Na O linear constraints and the O–Bi–O angular constraints.