Glassy dynamics and crystalline local order in two-dimensional amorphous silica

TL;DR

This study models two-dimensional amorphous silica, showing how local order and glassy dynamics relate, revealing two Arrhenius regimes and transient crystalline domains, which inform understanding of 2D glass structures.

Contribution

It reparameterizes an existing potential to match experimental structures and analyzes glassy dynamics and local order in 2D silica, highlighting the presence of two Arrhenius regimes.

Findings

Identification of two Arrhenius regimes separated by a crossover

Growth of bond-orientational order below crossover temperature

Presence of transient nanometric crystalline domains

Abstract

We reassess the modeling of amorphous silica bilayers as a two-dimensional classical system whose particles interact with an effective pairwise potential. We show that it is possible to reparameterize the potential developed by Roy, Heyde, and Heuer to quantitatively match the structural details of the experimental samples. We then study the glassy dynamics of the reparameterized model at low temperatures. Using appropriate cage-relative correlation functions, which suppress the effect of Mermin-Wagner fluctuations, we highlight the presence of two well-defined Arrhenius regimes separated by a narrow crossover region, which we connect to the thermodynamic anomalies and the changes in the local structure. We find that the bond-orientational order grows steadily below the crossover temperature and is associated to transient crystalline domains of nanometric size. These findings raise fundamental questions about the nature of glass structure in two dimensions and provide guidelines to interpret the experimental data.