Abstract
Enthalpy relaxation below and above the glass transition in an orientationally disordered crystal can be observed calorimetrically as a spontaneous temperature drift of the sample under an adiabatic condition. Upon the heating of a quenched sample, positive temperature drifts are observed to reach a peak at a temperature just below Tg and are followed by negative drifts on further heating. This behavior is the same as that for the glassy state of a liquid. Because of the high temperature stability in adiabatic calorimetry, analysis of the drift rate can produce quantitative relaxation time data when the relaxation involves a small amount of relevant enthalpy. Since the time scale is in the ultra-low frequency range, the results can be compared with other relaxation data obtained mainly by dielectric spectroscopy. Recent studies on some glassy crystals are here reviewed to show the wide variety of their freezing processes. Phenomena which can occur below the glass transition temperature will be discussed in relation to the Kauzmann's paradox.
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