Molecular Dynamics Simulations of Fluorozirconate Glass Structure

Abstract

The results of several different simulations of fluorozirconate glass structure using Molecular Dynamics modelling are compared. Most workers using this technique have concluded that Zr ions are on average in eightfold coordinated sites, whilst barium ions have coordination numbers between 10 and 11. ZrF8 coordination polyhedra are principally linked by corner sharing although edge sharing also occurs, the proportion varying somewhat between models. The role of stabilising ions (Al), modifier ions (Na and Li), and transition metal ions is considered and the model is also examined on the basis of a close packed arrangement of ions. The results are related to experimental studies of structure and to the observed behaviour of the melts and glasses, particularly diffusion coefficients, glass transition temperatures, free volume and density. Future possibilities for study include an extension of the use of the models to interpret structural information obtained by other techniques and a widening of the range of physical and thermodynamic properties modelled, both to provide extra physical insight and to improve the parameters used in the simulation.