Topological Origins of Flexibility and Internal Stress in Sodium Aluminosilicate Glasses

TL;DR

This study uses molecular dynamics to explore how sodium aluminosilicate glasses transition from flexible to stressed-rigid states, revealing that these transitions occur at different compositions and that the isostatic state exists within a composition window.

Contribution

It demonstrates the composition-dependent flexible-to-stressed-rigid transition and the non-coincidence of stress and flexibility transitions in sodium aluminosilicate glasses.

Findings

Flexible-to-stressed-rigid transition driven by composition.

Loss of atomic mobility correlates with internal stress onset.

Isostatic state exists within a composition window rather than at a threshold.

Abstract

In the framework of topological constraint theory, network glasses are classified as flexible, stressed--rigid, or isostatic if the number of atomic constraints is smaller, larger, or equal to the number of atomic degrees of freedom. Here, based on molecular dynamics simulations, we show that sodium aluminosilicate glasses exhibit a flexible-to-stressed--rigid transition driven by their composition. This transition manifests itself by a loss of atomic mobility and an onset of internal atomic stress. Importantly, we find that the flexible-to-rigid (i.e., loss of internal flexibility) and unstressed-to-stressed transitions (i.e., onset of internal stress) do not occur at the same composition. This suggests that the isostatic state (i.e., rigid but unstressed) is achieved within a window rather than at a threshold composition.