The structural properties of liquid and quenched sulphur II

Abstract

Neutron diffraction experiments over the momentum transfer range 0<Q(AA)-1<40 have been used to investigate the structural properties of liquid sulphur from 140 degrees C up to 300 degrees C, i.e. from conditions near the melting point of sulphur up to temperatures well above its lambda -transition (Tlambda =159 degrees C), and to study how the structure of sulphur rapidly quenched from different liquid temperatures changes in relation to the corresponding liquid structure. The data have been Fourier transformed to give an accurate pair correlation function g(r) from which absolute numbers and distances of atoms in given molecular configurations may be obtained. The results indicate which molecular bonds are changed in the different solid and liquid states and shed new light on the lambda -transition from a molecular point of view. In particular we show that the number of nearest neighbours probably increases with temperature above the lambda transition. The data on g(r) are also interpreted with recent reverse Monte Carlo calculations.

Short, intermediate and mesoscopic range order in sulfur-rich binary glasses

“…The S-S third neighbor distance in the orthorhombic a-sulfur crystal, c-S 8 , is 4.471 Å , while the fourth neighbors are situated at 4.718 Å . Similar feature was also observed in liquid sulfur below the polymerization transition, i.e., consisting of sulfur rings [23,24]. Consequently, the 4.5 Å peak was attributed to a weighted average of the 3rd and 4th neighbor distances in the sulfur rings.…”

Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water

“…This transition is believed to be due to the formation of long chains of sulphur atoms at the higher temperature. Yet the density barely changes in the transformation, (0.0335 atoms/Å 3 before to 0.0332 atoms/Å 3 after) and the diffraction patterns for sulphur in these two different states are almost identical [137]. Hence diffraction from a disordered material cannot by itself necessarily tell us the state of the material, unlike crystalline phases, where each phase has a distinct sequence of Bragg peaks.…”

Response to “Comment on ‘Probing in situ the sulfur polymerization transition with Raman spectroscopy’ ” [J. Chem. Phys. 121, 6573 (2004)]

“…Other neutron diffraction studies from the same group have also demonstrated structural differences between the liquid and the quenched solid. 13 This difference has been considered as arising from the existence of broken bonds in the quenched state. This unequivocally shows that depolymerization can occur during the quenching procedure.…”