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The work presented in this thesis is related to two different families of technological materials: optoelectronics and multiferroics. Our focus on these categories of materials was largely driven by an interest in growing highly crystalline epitaxial films by the Pulsed Laser Deposition technique and the anticipated thin film properties of smart materials, suitable for miniaturized electronic and energy devices. The thesis is structured in two parts. In the first part, the experimental investigation of SrZn1-xLixO2 as an optically transparent p-type material is discussed. Our work in this area was initially motivated by computational studies by Gupta et al.i on SrZnO2 as a host for p-type carrier and first-principles doping-dependent calculations indicating Li as the most promising p-type dopant. A range of dopants were experimentally tested by the conventional solid-state reaction and strictly anaerobic conditions and the successful substitution of Li+ for Zn2+ has been confirmed by combined PXRD and ICP studies. High quality ceramic samples of SrZn1-xLixO2 (0 < x < 0.06) were isolated and their structural, compositional and physical properties have been investigated. The p-type behaviour of SrZn1-xLixO2 was validated by thermopower and variable-pO2 resistivity measurements and found to be maintained for 40 days after storage in dry air, confirming the long-term stability of our p-type compounds. The synthesized SrZn1-xLixO2 samples were also found to retain the optical transparency of the parent SrZnO2 having a band gap of 4.27 eV, measured by UV-visible spectroscopy, in agreement with Gupta's calculations predicting a band gap of 3.80 eVi. It is worth noting here that this value supersedes the only previous report of SrZnO2 band gap of 3.41 eVii. Attempts to grow single-phase SrZnO2 films under variable growth conditions by PLD were unsuccessful. The main results of this work are currently under submission. In the second part of this thesis, our attention was focused on (1-x)BiTi(1-y)/2FeyMg(1-y)/2O3-xCaTiO3 (BTFM-CTO), a single-phase room temperature multiferroic stabilized at the morphotropic phase boundary between the rhombohedral [111]p and orthorhombic [001]p phases. The material exemplifies a doping strategy has been developed by Rosseinsky's group towards a lead-free and ambient-pressure bismuth-based phase demonstrating a long-range polarization along both the rhombohedral [111]p and orthorhombic [001]p phases. Investigating the room temperature properties of the x = 0.15 and y = 0.75 composition, Mandal et aliii succeeded to measure polarization of 66 μC/cm2, a saturated magnetization of 0.0097 ???? per Fe and a linear magnetoelectric susceptibility of 0.19(1) ps/m. In this thesis, our work was focused on the epitaxial growth of 0.85BiTi0.1Fe0.80Mg0.1 - 0.15CaTiO3 thin films on single crystal substrates of SrTiO3 and the investigation of their ferroelectric and magnetic properties. The multi-cation nature of the targeting compound required the precise control of the deposition process and the epitaxial growth of morphotropic (1-x)BiTi(1-y)/2FeyMg(1-y)/2O3-xCaTiO3 was only possible in a narrow window of growth conditions, identified by the combined use of elemental analysis (EDX/SEM) and structural (XRD) studies. Small deviations from this optimum set of growth conditions resulted in impurity phases. The coexistence of the two-phase regime in the as-deposited films was initially observed as a peak splitting of their out of plane (00l)PC pseudocubic reflections and later verified by detailed rocking curve measurements revealing the presence of two well-distinct crystalline phases. Reciprocal space maps confirm the coherent morphotropic film growth along different in plane crystallographic directions and their in-plane stretching to the SrTiO3 substrate. The crystalline structure of BTFM-CTO films was also found to be sensitive to epitaxial constraints. A higher lattice mismatch between ultra-thin (20 nm) BTFM-CTO films and the LaAlO3 substrate resulted in the growth of a single tetragonal-like phase, relaxed to a mixture of tetragonal and morphotropic (O+R) phases at higher thickness. To study the electrical properties of BTFM-CTO films parallel-plate capacitors were fabricated with the growth of a SrRhO3 buffer layer as bottom electrode and sputtered with Pt acting as top electrode. Dielectric measurements have shown the insulating (? 1.6 GO) and low losses nature of BTFM-CTO films. Room-temperature PE hysteresis loops measurements revealed the ferroelectric properties of BTFM-CTO films with a remanent ????????(??????)???? polarization exceeding 130 μC/cm2 under an applied voltage up to 25 V. These values were found to be much larger than those measured on bulk BTFM-CTO as a result of the preferential film orientation. The dielectric and ferroelectric properties of BTFM-CTO films were also found to depend on the morphotropic nature of the deposited films and samples failed to grow in the phase transition region have shown a shown a lossy, non-ferroelectric behaviour. Temperature dependent M(T) magnetisation and isothermal field-dependent magnetization M(H) measurements showed a substantially different magnetic behaviour of BTFM-CTO films to that of bulk samples with a strongly magnetized ferromagnetic iron-based impurity dominating the overall magnetic response of the films and hindering the weak ferromagnetic response of BTFM-CTO films.

This thesis will present the work conduced in the field of heterogeneous catalysis. This will mostly pertain to the TiO₂ system and the modification of such systems by the addition of platinum group metals (PGM). A fundamental study of the P25 TiO₂ system was undertaken and results showing the effect of multiple variable on catalytic activity are presented along with thorough characterisation of the anatase-rutile TiO₂ P25 system. Work on various synthetic methods is also presented. This consists of samples impregnated with PGM salts, prefabricated nanoparticles dispersed onto TiO₂ and flame spray pyrolysis synthesis of TiO₂ doped with both rhodium and erbium. These systems were explored by means of X-ray analysis and optical measurements before catalytic testing was conducted. In this section a method for rapid screening of doped TiO₂ by flame spray pyrolysis is discussed and the merits of such a system demonstrated. Extensive work has been conducted on the rhodium TiO₂ system. Pertaining to the solid state and the sol-gel synthetic routes of RhₓTi₁₋ₓO₂. The solid state system was studied and optimised before X-ray and optical experimentation was conducted to prove doping had occurred. From this the reduction and oxidation of the samples was studied. Using this as a model system evidence of Rh migration out of the TiO₂ lattice during reduction and oxidation was explored. A study of the sol-gel synthesis of RhₓTi₁₋ₓO₂ was also conducted. In this study optimisation of the synthetic system was undertake looking specifically at the pH of the sol and the subsequent calcination of the material. The triphasic nature of samples fired between 500-600 °C was studied and a series of doped RhₓTi₁₋ₓO₂ were produced and the phases produced during such calcination monitored as a function of temperature.

This thesis reports the synthesis and characterisation of a number of new Li-ion conductors with olivine and NASICON structure types. The new materials have been characterised by chemical analysis, diffraction and spectroscopy in order to establish relationships between the Li-ion conductivity and the crystal structure. The thesis starts describing Li-ion battery technology. The role of ceramic materials in battery development is highlighted and some of the state-of-the-art materials are introduced. The battery failure mechanism and fire risk are examined. Then defect chemistry and ionic conduction are presented to end with a literature review on families of Li-ion conductors indicating their conductivities and crystallographic features. The experimental techniques used throughout the thesis for the synthesis and characterisation of the new materials are also introduced. A large fraction of the work in the thesis focuses on the olivine-type structure of general composition LiMPO4 with M a 2+ cation. The main strategy developed in these chapters was the aliovalent substitution on M site in order to introduce Li-vacancies in the Li-ion diffusion pathways of the structure. A number of new modifications are reported, mainly based on the olivine material LiMgPO4. These series follow Vegard’s law up to a doping limit after which a plateau is reached. The impurity phases that appear in the plateau have been determined. In general, the synthesis of these new materials have needed higher temperatures than the parent phases, highlighting in this way the role of the entropy of mixing in this type of modification. Li-ion conductivity derived from AC impedance measurements are presented for some of the new samples. The rest of the work in the thesis is on the NASICON-type structure. A number of Li-ion analogues related to LiTaAl(PO4)3 have been investigated. The role of Li and P excess in the distortion of the unit cell has been studied with X-ray diffraction. For one of the related analogues, its phase diagram has been explored in a search for new Li-ion conductors with the NASICON-type structure. Densification methods to enable conductivity measurements have also been developed. Finally, Li-ion conductivity has been determined by AC impedance spectroscopy on a number of new phases. A summary chapter at the end of the thesis summarises the work and highlights the main conclusions and future directions.

As stated earlier in the title, the overall aim of the project has been to investigate “Synthesis, Characterisation and Photocatalytic Application of Rhodium-doped Oxides upon Irradiation with Visible Light”. The key considerations in photocatalyst design, assessment and challenges and energy requirements in application is reviewed in the Introduction chapter. In the Discussion chapters, first, a simple one-step strategy was employed to produce a high surface area, phase pure metal oxide that is active in UV light. Various structures have been produced as parent phases such as SrTiO3, BaTiO3 and Y2Ti2O7, and once the presence of phase pure material was confirmed, rhodium substitution was initiated by B site doping of structures by adding soluble Rh salts during phase formation. The idea of using rhodium was to provide active, new rhodium states within the band gap therefore induce e- and h+ transfer that will presumably facilitate photochemical reduction/oxidation reactions with a longer excited wavelength than 400 nm, visible light photons. The series of nanoparticulate SrTi1-xRhxO3 and BaTi1-xRhxO3 materials with x = 0; 0.01; 0.025; 0.050; 0.075 and 0.1 rhodium content have been fully characterised. The functionality of well-known SrTi1-xRhxO3 H2 generating p-type oxide was extended to be successfully applied in water remediation and disinfection with excellent performance in model Methyl Orange molecule degradation and reasonable efficiency in E. coli Gram-negative bacteria inactivation when exposed to visible light (λ > 420 mm). So far, of semiconductor oxides, nitrogen-doped titania in particular have demonstrated activity under visible light in all three functionalities mentioned above, making this new finding very encouraging in the application of SrTi0.95Rh0.05O3 compound. As the investigation of novel advanced materials is crucial in the field, following up on this, a novel stable visible-light-driven photocatalyst (λ ≥ 450 nm) for water oxidation is reported. Rhodium substitution into the pyrochlore Y2Ti2O7 is demonstrated by monitoring the Vegard’s law evolution of the unit-cell parameters with changing rhodium content, to a maximum content of 3% dopant. Substitution renders the solid solutions visible-light active. The overall rate of oxygen evolution is comparable to WO3 but with superior light-harvesting and surface-area-normalized turnover rates, making Y2Ti1.94Rh0.06O7 an excellent candidate for use in a Z-scheme water splitting system and photoanode.

The work presented in this thesis focuses on the synthesis of long axis A-site ordered perovskites, which have ordered oxygen vacancies. The materials discussed have also been assessed as potential cathodes for solid oxide fuel cells (SOFCs), targeting an intermediate temperature (IT) SOFC operating range of 500 800 °C. In chapter 3 of this thesis, a 16ap phase (ap = 1 perovskite unit, ABO3-δ), Y2.24Ba2.28Ca3.48Fe7.44Cu0.56O21-δ, was first observed in a powder X-ray diffraction (PXRD) pattern that resulted from the attempted Cu doping of a 10ap phase (Y0.9Ba1.7Ca2.4Fe5 xCuxO13 δ). This phase was indexed as ap √2 × 16ap × ap √2 by selective area electron diffraction (SAED). Mössbauer spectroscopy identified that Fe3+ existed in three different coordination environments and a Rietveld refinement was carried out using combined powder synchrotron (S) XRD and powder neutron diffraction (ND) data. High Angle Annular Scanning Transmission Electron Diffraction (HAADF-STEM) confirmed the A-site ordering from the refinement. The 16ap phase exhibited good thermal stability, CO2 stability and chemical compatibility with state of the art electrolytes (GDC, SDC and LSGM), as well as a close matching thermal expansion coefficient (TEC) with the same electrolytes. Although possessing low electronic conductivity, 3.5 S.cm-1 at 750 °C, a good area specific resistance (ASR) of 0.12 Ω.cm2 at 750 °C was achieved, within the IT-SOFC operating range. In chapter 4, a 10ap phase, Y0.9Ca2.4Sr1.7Fe5O13-δ (YCSFO), was discussed. The space group Imma was identified from SXRD data, while the structure was closely related to brownmillerite. A Rietveld refinement carried out with the addition of SXRD data collected at the K absorption edge for Sr determined A-site ordering. The ASR of YCSFO was three times higher than that of the 16ap phase, highlighting the ordering of oxygen vacancies. The final phases investigated in chapter 5 of this thesis belong to a family of Co doped 10ap phases (Y0.9Ba1.7Ca2.4Fe5 xCoxO13 δ). A range of compositions were synthesised by varying the cation ratios, in order to obtain high Co content phase pure samples. The highest Co content was x = 1.85 for compositions Y1.24Ba1.85Ca1.91Fe3.15Co1.85O13-δ (annealed in O2) and Y1.6Ba1.8Ca1.6Fe3.15Co1.85O13-δ. AC impedance measurements carried out showed that increased Co content reduced the ASR, with the values at 700 °C of 0.19 Ω.cm2 and 0.23 Ω.cm2 respectively.

The objective of this thesis was to develop and prepare multifunctional magnetic nanoparticles with targeting and bimodal imaging capabilities for cancer diagnostic applications. Superparamagnetic iron oxide nanoparticles (SPIONs) were the key component in the multifunctional nanoparticles prepared. In a first approach, alkoxysilane ligands were used to introduce functional groups such as amino, bromo, iodo, nitrile, and vinyl on the surface of SPIONs. Physicochemical analyses showed that each silane ligand formed a dense silane monolayer covalently attached to the nanoparticle surface. The amino-functionalised SPIONs were successfully modified yielding amino and carboxylic acid-bifunctionalised SPIONs using a succinylation reaction. This nanoparticle system showed no cytotoxicity during cell viability evaluations. Further conjugation with fluorescent dye and antibodies produced targeted bimodal optical/magnetic resonance imaging (MRI) agents, confirmed by good contrast enhancement capabilities. The conjugated antibody successfully enabled the targeted delivery of SPIONs to pancreatic cancer cells in vitro. The targeting efficiency and the nanoparticle cellular uptake were monitored using fluorescence and confocal microscopy. In a second approach, hydrophobic and monodisperse SPIONs were coated with amphiphilic polyoxazoline to produce colloidally stable magneto-micelles. This magneto-micellar system showed high colloidal stability in water, phosphate buffered saline as well as at different pH values. Fluorescent dyes were successfully co-assembled into the magneto-micelles providing for the localisation of the nanoparticles in the cells by confocal microscopy. Antibodies conjugated to nontoxic magneto-micelles allowed for binding to specific receptors present on pancreatic cancer cells. The targeting efficiency and accumulation of the antibody labelled magneto-micelles into pancreatic cancer cells was evaluated using live cell confocal microscopy. Their performance as MRI contrast agents was evaluated using relaxivity measurements and it was shown that the clustering effect of the SPIONs within the core of the micelle is particularly favourable for enhancing the contrast on MRI images. Both approaches provided efficient routes of preparation of multifunctional platforms to achieve the desired targeting and bimodal imaging capabilities.

This thesis describes the synthesis and application of complex metal oxide nanoparticles. The work is focussed on three core areas; the synthesis of CoFe2O4 nanoparticles and their application as CO oxidation catalysts, the controlled assembly of functionalised CoFe2O4 and BaTiO3 nanoparticles and the preparation and characterisation of magnetoelectric composites from chemically-bonded nanoparticle assemblies. Chapter 1 gives an introduction to the history of nanotechnology, recent developments in the synthesis of nanoparticles and other areas key to the work described herein. In Chapter 2 details the synthetic and analytical techniques employed. Chapter 3 describes the synthesis and characterisation of CoFe2O4 nanoparticles, and their application as catalysts in the CO oxidation reaction. Nanoparticles were prepared with a range of controlled sizes and were found to be active CO oxidation catalysts. Analysis of their size-dependent activity and stability is performed. Chapter 4 describes the assembly of CoFe2O4 and BaTiO3 nanoparticles by direct functionalisation of the nanoparticle surfaces using complementary organic functional molecules. Characterisation of the functionalised nanoparticles and assemblies is performed, and the extensibility of the developed functionalisation and assembly protocol is tested using particles with different sizes and morphologies. In Chapter 5 the assembled nanoparticles discussed in Chapter 4 are processed into dense ceramics with a view to preparing magnetoelectric composites. The magnetoelectric properties are tested, and optimisation of the ceramics is performed by modification of the starting nanoparticle sizes, composite composition and processing conditions. The composites are tested against control samples prepared by traditional grinding and firing, and characterisation of the ceramics using XRD and electron microscopy provides and insight as to why their magnetoelectric properties differ to those prepared by the traditional technique. The work contained in this thesis has been published in the following papers: - G. Evans, I. V. Kozhevnikov, E. F. Kozhevnikova, J. B. Claridge, R. Vaidhyanathan, C. Dickinson, C. D. Wood, A. I. Cooper, M. J. Rosseinsky, “Particle-size Activity Relationship for CoFe2O4 Nanoparticle CO Oxidation Catalysts,” J. Mater. Chem. 2008, 18, 5518. G. Evans, G. V. Duong, M. J. Ingleson, Z. Xu, J. T. A. Jones, Y. Z. Khimyak, J. B. Claridge, M. J. Rosseinsky, “Chemical Bonding Assembly of Multifunctional Oxide Nanocomposites,” Adv. Funct. Mater. 2010, 20, 231.