Room temperature plasticity in amorphous SiO₂ and amorphous Al₂O₃: A computational and topological study

Requirements for room temperature plasticity in oxides glasses have been only recently established. While atomistic mechanisms of this type of plasticity have been reported, it remains challenging to translate this knowledge between different structures and predict what other oxide glasses can be ductile and by which principle. Here we show that a coarse-grained analysis at the polyhedral level gives valuable information to accompany the atomistic characterization of plasticity, and we propose the analysis of polyhedral neighbor change events (PNCE) as a tool to allow comparison of the room temperature plasticity in various oxide glasses. Classical atomistic simulations with around 1 million atoms provided primitive data for coarse-grained analysis. Based on the PNCE analysis, the edge-sharing polyhedra are found to be up to 2 orders of magnitude more active in enabling plasticity, and combined with the occurrence of edge-sharing polyhedra, is shown to explain the brittle to ductile transition in a-SiO₂ and the intrinsically high ductility of a-Al₂O₃. Finally, the coarse-grained analysis enables the benefit of using additional topological constraint theory analysis to yield more in-depth information regarding the ductile features of each glass structure. Quantitative comparison between amorphous Al₂O₃ and SiO₂ shows a consistent trend between the materials and shows that the approach can be extended to the designing of other damage tolerant oxide glass materials.