Self-diffusion in calcium aluminosilicate glasses was investigated at the atomistic level using molecular dynamics simulations. A study was made of nine glass compositions having a fixed ratio, CaO]/[Al2O3 = 1, where the concentration of SiO2 was varied from 11.8 to 76.5mol%. The diffusion coefficient was calculated for each composition at 300 to 6000K, in steps of 300K. The self-diffusivities of the various elements were found to be close to each other in magnitude, reflecting the cooperative nature of the atomic movement. Network so-called defects such as miscoordinated cations, non-bridging oxygen and oxygen triclusters were also studied as a function of temperature and composition. It was found that the self-diffusion behavior was closely correlated to the concentration of network defects. A model for self-diffusion in calcium aluminosilicate glasses was proposed in which diffusion was considered to be a defect-mediated process resulting from bond-switching reactions at high temperature.

Defect-Mediated Self-Diffusion in Calcium Aluminosilicate Glasses: a Molecular Modelling Study. Tandia, A., Timofeev, N.T., Mauro, J.C., Vargheese, K.D.: Journal of Non-Crystalline Solids, 2011, 357[7], 1780-6