Topological hardening through oxygen triclusters in calcium aluminosilicate glasses

Molecular dynamics simulations and topological constraint theory are used to study the impact of oxygen triclusters in the calcium aluminosilicate glass system at ratios of 0.6, 1, 1.5, 2, and 4 [Al₂O₃]/[CaO]. Negligible percentages (less than ~3%) of five-coordinated Al structures are found at all ratios. Up to ~27% three-coordinated oxygens, also known as triclusters, are found at the highest ratio of [Al₂O₃]/[CaO]. A topological constraint model, which considers additional constraints provided by triclusters, is created to predict the glass transition temperature, hardness, and Young's modulus. The models are used to elucidate the role of triclusters in glass properties. Analysis of topological constraints shows that triclusters can potentially increase the glass hardness within the calcium aluminosilicate system. The results are also compared to oxynitride glasses. Triclusters show the same ability as nitrogen to increase the glass hardness but are less effective at increasing the Young's modulus.