Elaboration of entropy with glass composition: A molecular dynamics study

Recently, entropy was proposed as a simple input into glass science and engineering, which has an interesting relationship with the glass properties containing glass transition temperature (T g ), melting point, and concentration of non-bridging oxygens (NBOs). In the current study, molecular dynamics (MD) simulation as the powerful method was used to approve the recently observed relations. In this regard, various silicate-based compositions containing 25, 30, and 35 mol% of alkaline earth oxides were simulated. The T g , bond length, and the concentration of NBOs were evaluated using MD simulation results, including volume-temperature curves and radial distribution functions (RDF) results. According to the results, T g values of the simulated glass were reduced up to 400 K by increasing the amounts of additives up to 35 mol%. The distance between Si and O species as the glass former basis increased from 1.580, 1.591, 1.608, and 1.615 Å to 1.590, 1.596, 1.616, and 1.621 Å, in the SsiO 2 -MgO, SiO 2 -SrO, SiO 2 -CaO, SiO 2 -SrO, and SiO 2 -BaO systems, respectively. Besides, as found from the results, increasing the concentration of additives increases the mobility of Si-O paired atoms. Accordingly, the glass disorderliness or entropy of the systems increases with adding glass modifiers. Also, the concentration of NBOs in the mentioned systems was 35.9-56.3, 36.8-57.5, 26.1-43.9, and 18.2-29.7%. The results of NBOs confirm that the glass disordering increases by increasing amounts of additives. In summary, using MD simulation of silicate glass containing alkaline earth oxides, the relation between entropy as a theoretically calculated property and glass characteristics such as T g is successfully approved.