Is the Fragility of a Liquid Embedded in the Properties of its Glass?

TL;DR

This paper explores how the microscopic vibrational properties of glasses, well below the glass transition temperature, are correlated with their fragility, extending the concept of fragility from liquids to the glassy state.

Contribution

It demonstrates a correlation between vibrational properties of glasses below T_g and their fragility, proposing a method to determine fragility from glass properties.

Findings

Vibrational properties below T_g are correlated with fragility.

Fragility can be extended and determined from glass properties.

Experimental evidence links microscopic glass features to macroscopic fragility.

Abstract

When a liquid is cooled below its melting temperature it usually crystallizes. However, if the quenching rate is fast enough, it is possible that the system remains in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes "solid" for any practical purpose, and this defines the glass transition temperature $T_g$. Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and, accordingly, they have been classified introducing the concept of "fragility". We report experimental observations that relate the microscopic properties of the {\it glassy phase} to the fragility. We find that the vibrational properties of the glass {\it well below} $T_g$ are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below $T_g$.