Neutron diffraction studies of phosphorus

Neutron diffraction measurements have been made on a sample of white phosphorus in the normal liquid and supercooled liquid states at temperatures of 10, 20, 30 and 50°C. The measured structure factor S M(Q) has been converted to a pair distribution function d(r) which shows strong orientational correlations between adjacent molecules. The variation of temperature does not have a large effect on these correlations and the structural properties of the supercooled liquid at a temperature of 30° below the melting point are essentially the same as those of the normal liquid. Measurements have also been made for the solid α-phase at 20°C with two samples prepared in different ways. The diffraction pattern shows a few Bragg peaks at low Q-values and is typical of a plastic crystal phase in which rotational disorder reduces the long range correlations of the lattice. The peak positions are not consistent with the accepted cubic structure of α-phosphorus determined by X-ray studies, but there is insufficient information to formulate an alternative form.