Molecular dynamic simulation of heterogeneity and chemical states of fluorine in amorphous alkaline earth silicate systems

Chemical states of fluorine in fluorosilicate glasses in the system MF₂-MO-SiO₂ (M = Ca, Sr and Ba; SiO₂ content < 60 mol%) have been investigated by molecular dynamic (MD) simulations with a perfect ionic two-body potential. Comparison of the results with those derived by X-ray photoelectron spectra of the actual glasses demonstrates that MD simulations reproduce well the bonding states of fluorine in the systems as well as the formation of M-F clusters. The MD generated structure of imaginary glasses, or glasses not obtained by the conventional melt-quench technique, with 70 mol% SiO₂ indicates that an acidic environment induces a greater amount of F-Si bonds. Their M-F pair correlation functions plotted against normalized M-F distances suggest that relative ion positions in the clusters are very similar.