Peculiarities of the enthalpy relaxation of a glassy crystal Original Research Article

The relaxation of a supercooled orientational glassy crystal is investigated by differential scanning calorimetry. Aging performed both below and above Tg reveal two original features. (i) The glassy compound relaxes beyond the simple return to equilibration of the metastable rotator phase. The state which is reached upon aging however reverses back to the metastable state when crossing Tg. (ii) Upon reheating a transition between a low temperature ordered phase and the rotator phase is observed whose occurrence strongly depends on the aging conditions. The calorimetric signature of this transition and the usual glass relaxation endotherm are superimposed when annealing is performed below Tg. These results suggest that the peculiarities of the structure and dynamics of orientational glassy crystals lead to an effective acceleration of the relaxation process and enable the system to search for enthalpy states lower than it is usual for a glass.