Pressure-induced ordering in cyanoadamantane plastic crystal

Raman scattering investigations of cyanoadamantane plastic crystal in a narrow pressure range (0–1 GPa), reveal the evidence for a kinetic transformation of the disordered state under pressure towards an ordered high-pressure (H-P) phase. This latter is observed to be different from the ordered low-temperature phase. The ability of cyanoadamantane to be placed in a disordered metastable state on pressurization suggests the existence of a glass transition under pressure. The order–disorder phase transition was observed on the decreasing pressure range of 0.3–0.2 GPa. The close relation between the low-frequency Raman spectrum of the orientational glass obtain by rapid cooling of the plastic phase and the lattice modes of the ordered H-P phase could indicate that this latter is involved in the vitrification process of cyanoadamantane.