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