Metastability and Instability in an Orientational Glass
Molecular crystals offer a large variety of disordered systems. Specially interesting are those in which an average translational order is preserved allowing to focus on the dynamic orientational disorder. This paper will concentrate on non equilibrium properties of such a system after a quench. The situation is thus relevant to non-diffusive first-order transformation kinetics and to orientational glassy behaviour if the quench is deep enough. A temperature time X-Ray analysis1 will be reviewed which allows to characterise the kinetics and molecular mechanisms involved both in the aging and the glass like transition of cyanoadamantane (CN-ADM). Very recent results will be presented in brief at the end of the paper. These concern a new system of a mixed crystal of the CN-ADM and chloroadamantane (Cl-ADM). Under appropriate time temperature treatment the latter shows apparent escape and come back to metastability.
KeywordsBragg Peak Mixed Crystal Molecular Crystal Molecular Dipole Classical Nucleation Theory
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