Short-range-order correlations in the orientationally disordered phase of hexachloroethane. I. Diffuse X-ray scattering

Abstract

Diffuse X-ray scattering has been measured in the orientationally disordered phase of C2C16 at 453 K. A model structure, which was generated in a Monte Carlo program, reproduces the dominant singlemolecule part of the diffuse scattering. In addition the existence of a one-dimensional orientational order along the body diagonals ofthe cubic lattice is demonstrated. The related planes of diffuse scattering are calculated in terms of the Naya model [Naya (1974).

Structural correlations in disordered matter: An experimental separation of orientational and positional contributions

“…2 , where b i stand for the nuclear coherent scattering lengths͔ are thus represented up to a reasonably good level of accuracy by a sum of plane ͑Bragg͒ and sphericalwave ͑diffuse͒ components, [12][13][14][15] …”

“…Our approach instead proceeds in a stepwise manner, separating first the Bragg profile from the total S(Q) by means of Rietveld analysis. The analysis of S Bragg (Q) then proceeds along established routes 13,15 and provides information about the underlying crystal lattice. The difference S(Q)ϪS Bragg (Q) gives…”

“…from where subtraction of a f 1 (Q) form factor will provide the function S diff c (Q) plus a term f 2 (Q)exp(Ϫ2W) which as shown by Gerlach and Prandl 15 will contain contributions arising from the uncorrelated vibrations ͑translational͒ of the average molecule. Because of the Debye-Waller factor which gives mean-square amplitudes of about 0.17 Å 2 , the latter function will decay quite fast having attained rather small values above Qу4Ϫ5 Å Ϫ1 .…”

Short-range-order correlations in the orientationally disordered phase of hexachloroethane. II. Elastic and quasielastic neutron scattering

“…In the first part (Gerlach & Prandl, 1988, hereafter referred to as I), we analysed the diffuse X-ray scattering. We were able to distinguish between singlemolecule scattering and contributions to the diffuse scattering having a more-pronounced variation of *Present address: Institut ffir Experimentalphysik der Universitat Kiel, Olshausenstrasse 40, D-2300 Kiel 1, Federal Republic of Germany.…”

Competing structures within the first shell of liquid C2Cl6: A molecular dynamics study

“…For the structure of the plastic phase Gerlach et.al [15] conducted a neutron powder and Single-Crystal investigation and later Gerlach et.al [16] compared the previous results to a model structure of the plastic phase from a Monte Carlo (MC) method. In 1988 Gerlach and Prandl [17] studied the orientational ordering in the plastic phase using diffuse X-ray scattering and later (Gerlach et al [18]) with elastic and quasielastic neutron scattering. Criado and Muñoz [19] used MD to simulate the plastic phase of C 2 Cl 6 and used the results to interpret an inelastic neutron scattering experiment [20].…”