Prigogine-Defay ratio of glassy freezing scales with liquid fragility

TL;DR

This study reveals that the Prigogine-Defay ratio in glassy materials correlates with liquid fragility, approaching 1 for fragile liquids and exceeding 20 for strong ones, linked to a hidden phase transition.

Contribution

It uncovers a novel relationship between the Prigogine-Defay ratio and liquid fragility, explaining the variation through a hidden phase transition.

Findings

R approaches 1 for high fragility index m

R exceeds 20 for low fragility index m

Correlation explained by separation of glass transition from hidden phase transition

Abstract

A detailed study of published experimental data for a variety of materials on the incremental variation of heat capacity, thermal expansion, and compressibility at glassy freezing reveals a striking dependence of the Prigogine-Defay ratio R on the fragility index m. At high m, R approaches values of ~1, the Ehrenfest expectation for 2nd order continuous phase transitions, while R reaches values > 20 for low fragilities. We explain this correlation by the degree of separation of the glassy freezing temperature from a hidden phase transition into an ideal low-temperature glass.