Harunsani, Mohammad H. (2013) Characterisation of mixed-metal oxides prepared by hydrothermal synthesis. PhD thesis, University of Warwick.

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Abstract

Mixed-metal oxides were prepared via hydrothermal synthesis and
characterised using various analytical techniques. Three different class of materials
were studied, namely perovskites, hexagonal perovskites and doped TiO2. By using
hydrothermal synthesis, control on the crystal size, morphology and phase purity was
achieved, which are difficult by conventional methods.
A new titanate perovskite solid solution with nominal composition,
NaCe1-xLaxTi2O6, containing three different metals on the A-site was produced by a
single step hydrothermal synthesis. Rietveld analysis of powder X-ray and neutron
diffraction data enabled the space group R c to be assigned for the whole series. The
particle size and morphology can be changed by varying the solvent and NaOH
concentration. 23Na MAS NMR showed that a genuine solid solution was produced,
with no A-site ordering present, while 2H MAS NMR of the samples prepared in
D2O showed the inclusion of D2O in the lattice in place of Na, greatest for the
cerium-containing materials, in which oxidation to Ce4+ can occur.
The preparation of B-site substituted perovskites was possible via
hydrothermal synthesis. The effect of substituting Zr for Ti was studied for two
different perovskites namely NaLaTi2O6 and NaBiTi2O6. For NaLaTi2O6, Zr
substitution had a drastic effect on the crystal morphology. Other factors that can
affect the morphology such as the solvent, reaction time, temperature and NaOH
concentrations were also investigated. In the case of NaBiTi2O6, the effect of Zr
substitution on ferroelectric and piezoelectric properties was studied.
Pure hexagonal YMnO3 was achieved by a comproportionation hydrothermal
reaction between KMnO4 and MnCl2. The possibility of doping YMnO3 with Fe was
investigated. Fe doping up to 10% was possible but above this level, impurity phases
were observed. Pure orthorhombic YFeO3 can also be prepared and the Fe3+ was
replaced by up to 30% Mn3+. The oxidation states of these materials were determined
using XANES.
Phase pure rutile TiO2 was prepared via two different hydrothermal routes.
Attempts at doping W into TiO2 were only achieved at 1% W doping level. With Sn,
a rutile Sn-TiO2 complete solid solution is formed. In contrast, Ce-TiO2 with up to
15% Ce is formed as the anatase structure with a mixture of Ce3+ and Ce4+. The
photocatalytic properties of the Ce-TiO2 materials show promise for high activity
hydrogen production by UV splitting of water.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Metallic oxides -- Synthesis, Thermochemistry, Perovskite -- Synthesis, Titanium dioxide -- Synthesis
Official Date:	September 2013
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Walton, Richard I.
Sponsors:	Brunei. Ministry of Education
Extent:	v, 261 leaves : illustrations, charts.
Language:	eng

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