title: Order-disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction.
abstract: High-resolution neutron powder diffraction has been used in order to characterize the order-disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc=198.4 (3) K, and a critical exponent, beta=0.28 (3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed.
authors.affiliation: ISIS Facility, CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, England.
authors.forename: W I F
authors.initials: WI
authors.lastname: David
authors.forename: R M
authors.initials: RM
authors.lastname: Ibberson
authors.forename: S F J
authors.initials: SF
authors.lastname: Cox
authors.forename: P T
authors.initials: PT
authors.lastname: Wood
mesh_terms: D008958:Models, Molecular; D033363:Neutron Diffraction; D033362:Powder Diffraction; D012680:Sensitivity and Specificity; D013455:Sulfur / Q000737:chemistry*; D013696:Temperature
chemical_list: D013455:Sulfur