The structural properties of liquid, solid and amorphous sulphur

Abstract

A series of neutron diffraction experiments have been used to investigate the properties of liquid, solid and amorphous sulphur. The liquid was studied from 131 degrees C to 230 degrees C, i.e. at conditions around the λ -transition (Tλ=159 degrees C). The amorphous sample was studied at -196 degrees C and the crystalline solid at room temperature. The data have been transformed to give an accurate pair correlation function g(r) from which the absolute numbers of atoms in given molecular configurations may be determined for distances less than 8 AA. A comparison of the solid and liquid g(r) data indicates which intermolecular bonds are broken on melting. The liquid data seem to be inconsistent with the picture of 'crown'-shaped S8 molecules below Tλ , and with the proposed S8-to-polymer transition at Tλ. Also it has been found that the diffraction pattern may be analyzed as though the liquid was an assembly of roughly spherical molecular units. In this case each unit would contain about six atoms, and the λ-transition could be related to the percolation limit for these units. The amorphous material was studied at the quenching temperature of -196 degrees C and its structure is intermediate between that of the parent liquid and the crystalline solid. It is concluded that a fundamental diffraction analysis of the states of sulphur has thrown new light on long standing problems.