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Title: Investigating materials with disordered structures using total neutron scattering
Author: Playford, Helen Y.
ISNI:       0000 0004 2739 9197
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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The structures of a variety of disordered materials were determined using the technique of total neutron scattering. The synthesis of various polymorphs of Ga2O3 and related materials was investigated and the structures of the hitherto uncharacterised polymorphs were examined in detail. The structure of y-Ga2O3 was found to be a cubic defect spinel with four partially occupied Ga sites, however, the octahedral Ga coordination environments were found to be distorted from the average cubic structure. The cation distribution in y-Ga2O3 was found to depend on particle size and synthesis method. Examination of the structure of E-Ga2O3 revealed that it is analogous to a disordered, hexagonal form of E-Fe2O3. The poorly crystalline product of the thermal decomposition of Ga(NO3)3.9H2O was found to be a nanocrystalline modification of E-Ga2O3, rather than a distinct phase with the bixbyite structure, as had been previously reported. The structure of a novel gallium oxyhydroxide, Ga5O7(OH), was determined to be analogous to tohdite, Al5O7(OH), and in its thermal decomposition pathway was revealed a new Ga2O3 polymorph: orthorhombic K-Ga2O3. A solvothermal synthetic route to spinel structured ternary gallium oxides, of general formula MxGa3-xO4-y, was developed. The structures of the materials where M = Zn or Ni were found to be consistent with those previously published. The materials where M = Co or Fe possess novel, oxygen-deficient compositions and exhibit interesting magnetic behaviour. A series of cerium bismuth oxides of formula Ce1-xBixO2-1/2x were found to adopt the cubic fluorite structure with significant local distortion due to the preference of Bi3+ for an asymmetric coordination environment. A sodium cerium titanate pyrochlore was also structurally characterised and it was determined that, due to the presence of three different cations on the A site, the local structure required a model with reduced symmetry. In situ neutron scattering experiments were carried out on amorphous zeolite precursor gels in the presence of the reaction liquid. These experiments revealed structural features unique to the gel, and proved that the gel undergoes irreversible structural changes on drying. Preliminary analysis of the gel structure indicated that the Na+ cations play an important role in the development of the ordered zeolitic framework, and revealed no strong evidence for the existence of discrete structural building units in the gel.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; QD Chemistry