STRUCTURAL AND DYNAMIC PROPERTIES OF LIQUID SULFUR AROUND THE LAMBDA-TRANSITION

To gain a deeper understanding of the structure of liquid sulfur and t he nature of the lambda-transition at 159 degrees C, we have performed inelastic neutron scattering (INS) experiments to yield the vibration al density of states of polycrystalline alpha-and beta-sulfur and of l iquid sulfur at temperatures above (170 degrees C) and below (140 degr ees C) that of the lambda-iransition, T-lambda. The data are compared with Raman spectra taken at the same temperatures. The relative intens ities of the spectral features in the solid and liquid state show a si gnificant dependence on temperature. It is concluded that the structur e of molten sulfur is not describable in terms of the occurrence of di stinct stable molecules. Since the local structural and INS spectral p arameters for liquid sulfur below and above the lambda-transition temp erature differ only slightly, it can be inferred that the difference b etween these two states is due to different molecular species with sim ilar local packing properties but different thermal stabilities. A tem perature-dependent dynamical equilibrium model for the liquid state se ems appropriate, which might lead to a percolation transition around T -lambda = 159 degrees C. (C) 1998 Elsevier Science B.V. All rights res erved.