Phase transitions in triamantane

The triple-cage triamantane, C₁₈H₂₄, in addition to the previously-reported transition to a plastic pre-melting phase at 150°C, is now found to undergo a gradual transition from an ordered phase at 0°C to a disordered phase at 30°C involving an increasing proportion of molecules re-orienting about one axis. The mechanism for this transition is established and a disorder parameter defined and estimated at three temperatures from X-ray measurements.