Structural studies of cyclohexane C6D12 by neutron diffraction .3. Temperature variation measurements for the liquid and plastic crystal phases

Neutron diffraction measurements on C6D12 over a wide temperature range, covering liquid crystal, plastic crystal and brittle crystal phases, are presented. The data extend work conducted previously over a restricted temperature range and show that the structural features are dependent on the thermal history of the sample. The results demonstrate the relative contributions from lattice symmetry (ordered) and diffuse scattering (disordered) at varying temperatures. The spatial distribution function undergoes a complex change in which orientational correlations between adjacent molecules appear to be coupled to translational displacements of the molecular centres. Previous assumptions that cyclohexane is an 'almost-unhindered' rotator are found to be erroneous and the spatial correlations exhibit a complex relationship which is sensitive to temperature variation. Further methods for the analysis of the order-disorder features are considered.