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Neutron diffraction studies of ices

Lobban, Colin; (1998) Neutron diffraction studies of ices. Doctoral thesis (Ph.D), University of London. Green open access

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Abstract

This thesis reports on a series of neutron diffraction measurements on ices in the medium-pressure range of the phase diagram in order to address several outstanding issues. The structure of ice II under its thermodynamic conditions of stability is unknown. Previous studies have used helium gas as the pressurising medium, which is included within the ice structure. Argon gas has been used in this work as the pressure medium, and the detailed structure of ice II is presented and discussed. Similarly, the structure of ice V under its conditions of stability is established for the first time by this work. For ices III and V, the presence of orientational order is controversial with the results obtained from structural studies on recovered samples differing from conclusions drawn from dielectric and spectroscopic measurements. The results obtained in this work indicate partial ordering of the water molecules which, for ice V, appears to be both temperature and pressure dependant. Ice IV is a metastable phase of ice that is difficult to form. A structure has been proposed on the basis of samples recovered to ambient pressure at 110 K . This work has successfully prepared ice IV at high temperature and pressure and a structure refinement confirms, for the first time, that the proposed structure is correct. During studies within the established stability region of ice V, features were observed which could not be identified as any ice or clathrate phase. Further work in this region has successfully formed and retained one such phase. The structure has been solved and the phase identified as a new ice structure. The topology of this phase is unlike that of any known solid water structure, and contains a mixture of seven- and eight-membered rings. General issues concerning hydrogen-bonding, compressibility and expansivity of these phases are discussed.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Neutron diffraction studies of ices
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10065569
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