Thermodynamic and Kinetic Fragility of Freon 113: The Most Fragile Plastic Crystal

6 pags., 5 figs.We present a dynamic and thermodynamic study of the orientational glass former Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane, CCl2F-CClF2) in order to analyze its kinetic and thermodynamic fragilities. Freon 113 displays internal molecular degrees of freedom that 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.This work has been partially supported by the Spanish MINECO through Projects No. FIS2014-54734-P and FIS2014-54498-R and MAT2014-57866-REDT and “María de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0377). We also acknowledge the Generalitat de Catalunya under Project No. 2014SGR-581 and the Autonomous Community of Madrid through program NANOFRONTMAG-CM (S2013/MIT-2850).Peer Reviewe