Entropy favors heterogeneous structures of networks near the rigidity threshold

TL;DR

This paper investigates how entropy influences the formation of heterogeneous versus homogeneous structures in disordered networks near the rigidity threshold, revealing entropy's role in structural phase transitions relevant to amorphous materials.

Contribution

It demonstrates that vibrational entropy promotes heterogeneity near the rigidity threshold, offering a new understanding of structural transitions in amorphous networks.

Findings

Entropy increases heterogeneity near the rigidity threshold.

Stress-energy favors homogeneity at the glass transition.

Structural phase changes explain transitions in chalcogenide glasses.

Abstract

The dynamical properties and mechanical functions of amorphous materials are governed by their microscopic structures, particularly the elasticity of the interaction networks, which is generally complicated by structural heterogeneity. This ubiquitous heterogeneous nature of amorphous materials is intriguingly attributed to a complex role of entropy. Here, we show in disordered networks that the vibrational entropy increases by creating phase-separated structures when the interaction connectivity is close to the onset of network rigidity. The stress-energy, which conversely penalizes the heterogeneity, finally dominates a smaller vicinity of the rigidity threshold at the glass transition and creates a homogeneous intermediate phase. This picture of structures changing between homogeneous and heterogeneous phases by varying connectivity provides an interpretation of the transitions observed in chalcogenide glasses.