Structural signature of the configurational entropy change during the glass formation of plastic crystal cyanoadamantane

Calorimetric and x-ray diffraction experiments are combined to characterize the entrance of a cyanoadamantane plastic crystal into a glassy crystal st ate upon cooling. As usually observed for glass-forming liquids, the config urational entropy of this glassy crystal is shown to strongly decrease on a pproaching the glass transition. Taking advantage of the underlying lattice of this peculiar glass, we could identify the structural origin of this en tropy change. It corresponds clearly to the development of an antiferroelec tric short-range order which is the precursor of a transient metastable sta te recently described. The analysis of the results, in the framework of the Adam and Gibbs theory, provides a new picture of the cooperative processes expected in glasses. (C) 2000 American Institute of Physics. [S0021-9606(0 0)51224-0].