Playford, Helen Y. (2012) Investigating materials with disordered structures using total neutron scattering. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Neutrons -- Scattering, Gallium compounds
Official Date:	September 2012
Dates:	Date Event September 2012 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Walton, Richard I.
Extent:	xxv, 282 leaves : illustrations, charts.
Language:	eng

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