Ionic self-diffusion of Na2O–Al2O3–SiO2 glasses from molecular dynamics simulations

Abstract

The structure of alkali aluminosilicate glasses (NAS) as a function of the molar ratio of Al/Na (RAl/Na) were investigated by using classical molecular dynamics simulations and validated by comparing with the high energy X-ray diffraction experiments. General structural features, including the pair distribution functions, coordination number, Qn distribution, oxygen species and ring size distributions, were analyzed to elucidate the effects of Al content on the structure of the glasses. By inducing effective rings size as a new parameter, the RAl/Na dependence of the alkali ion diffusion ability below the glass transition temperature were analyzed on the basis of medium range structures instead of the calculated diffusion coefficient. The results suggest that the optimum aluminum content for NAS system exists at around RAl/Na = 1.2 not only with a high ionic self-diffusion but also with a good network connectivity, providing a theoretical guidance for the design and optimization of chemically strengthened glasses.