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Title: X-ray diffraction studies of complex high-pressure phases of Bi, Sb, As, and Ga
Author: Degtyareva, Olga
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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The work presented in this thesis applies advanced high-resolution powder diffraction techniques in combination with novel single-crystal diffraction techniques, recently developed in the Edinburgh High-Pressure Group, to studies of complex HP phases of group-V elements and Ga. The HP phases Bi-III and Sb-II, a subject of many experimental studies in the past and present, are shown to have an incommensurate host-guest structure, similar to that found in alkaline-earth elements. The basic host-guest structure is shown to be modulated, and a single-crystal diffraction study on Bi-III has revealed the true from of the modulation between the host and guest components. From HP powder diffraction studies of Sb, a new incommensurate host-guest phase Sb-II* is discovered, and a novel incommensurate to incommensurate phase transition is observed. The HP phase As-III is solved from powder diffraction data as a modulated incommensurate host-guest structure, and is shown to be the same as Sb-II*. Four-dimensional formalism is applied to the crystallographic description of these incommensurate phases. The group-III element Ga is known to have a complex HP behaviour with metastable effects and several phase transitions. The structure of the HP phase Ga-II was long believed to be cubic with 12 atoms in the unit cell but is shown from single-crystal diffraction data to be orthorhombic with 104 atoms in the unit cell. A new HP phase is discovered to be stable in Ga above the Ga-II phase, and its structure is solved from powder diffraction techniques as rhombohedral with 6 atoms in the unit cell, which represents a new structure type of an element. A revised phase diagram of Ga is proposed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available