The polymorphism of carbon tetrachloride

A peculiarity of the polymorphic transition of CCl4 was first observed by Rudman and Post (1) using X-ray and optical studies in 1966. They found that on cooling CCl4 from the melt, a face-centred cubic phase is formed. However, this face-centred cubic phase or phase I is transformed spontaneously to a rhombohedral or phase II if left at this temperature for a few hours. This rhombohedral phase is then followed by a transformation to a monoclinic phase or the glassy phase III. On warming of the glassy phase, the rhombohedral phase is formed and this phase persists until it melts.