The orientational glassy state and glass transition in cyanoadamantane: kinetics of metastable ordering and cluster reversion

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Abstract
Temperature-time measurements on single glassy crystals of cyanoadamantane trace the structural mechanism of annealing and orientational glass transition. Relaxation in the glassy state operates by development of antiferromagnetic orientationally ordered microclusters which are well resolved. The associated kinetics involve nonconserved order parameters. One observes two distinct regimes seemingly related to metastable and unstable states. Correlated coherency strains progressively break the underlying cubic symmetry. A parallel contraction is observed. The structural mechanism of the glass-like heat absorption when heating is the reversion of clusters and the restoration of the homogeneous cubic disordered state. The blocking role of clusters in the orientational freezing is conjectured.