Direct evidence of rigidity loss and self-organisation in silicate glasses

TL;DR

This study provides direct evidence of rigidity transitions and self-organization in sodium silicate glasses by analyzing elastic energy changes and calorimetric data, revealing distinct floppy, stressed-rigid, and intermediate phases.

Contribution

It offers the first direct measurement linking elastic energy changes to rigidity phases and identifies an intermediate phase in sodium silicate glasses.

Findings

Elastic free energy change decreases linearly in the floppy phase.

Nearly vanishes in the stressed-rigid phase.

Intermediate phase shows minimal non-reversing enthalpy.

Abstract

The Brillouin elastic free energy change $DF$ between thermally annealed and quenched $(Na_2O)_x(SiO_2)_{1-x}$ glasses is found to decrease linearly at $x > 0.23$ (floppy phase), and to nearly vanish at $x < 0.18$ (stressed- rigid phase). The observed $D F(x)$ variation closely parallels the mean-field floppy mode fraction $f(x)$ in random networks, and fixes the two (floppy, stressed-rigid) elastic phases. In calorimetric measurements, the non-reversing enthalpy near $T_g$ is found to be large at $x < 0.18$ and at $x > 0.23$, but to nearly vanish in the $0.18 < x < 0.23$ range, suggesting existence of an intermediate phase between the floppy and stressed-rigid phases.