Thermodynamic and kinetic fragility of Freon113: the most fragile plastic crystal

TL;DR

This study investigates the thermodynamic and kinetic fragility of Freon113, revealing it as the most fragile orientational glass former with complex energy landscape features and low-energy excitations.

Contribution

It provides a comprehensive analysis of Freon113's fragility, combining experimental specific heat, vibrational density of states, and dielectric spectroscopy, challenging previous correlations between boson peak and specific heat.

Findings

Freon113 exhibits the highest thermodynamic and kinetic fragility among orientational glasses.

Presence of glassy low-energy excitations evidenced by boson peak and excess specific heat.

Counterexample to the correlation between boson peak and Debye specific heat.

Abstract

We present a dynamic and thermodynamic study of the orientational glass former Freon113 (CCl2F-CClF2) in order to analyze its kinetic and thermodynamic fragilities. Freon113 displays internal molecular degrees of freedom which promote a complex energy landscape. Experimental specific heat and its microscopic origin, the vibrational density of states from inelastic neutron scattering, together with the orientational dynamics obtained by means of dielectric spectroscopy have revealed the highest fragility value, both thermodynamic and kinetic, found for this orientational glass former. The excess in both Debye-reduced specific heat and density of states (boson peak) evidences the existence of glassy low-energy excitations. We demonstrate that early proposed correlations between the boson peak and the Debye specific heat value are elusive as revealed by the clear counterexample of the studied case.