The effects of low concentration Co, Cr and Mn oxide, singly and in combination, on the sintering and electrical properties of Ce0.9Gd0.1O1.95 (CGO) have been investigated with possible mechanisms suggested to explain this modified behaviour. The influence of these dopants on the densification kinetics of CGO were primarily investigated using constant heating rate dilatometry. Whilst low concentration Co and Mn-oxide were found to improve the sinterability of CGO, the addition of Cr-oxide was found to inhibit the densification kinetics of the material. The location and concentration of these dopants were investigated as a function of relative density using scanning transmission electron microscopy combined with energy dispersive x-ray mapping. All materials showed a gradual reduction in the grain boundary dopant concentration with sintering time, leading eventually to the formation of a second phase that was subsequently analysed by either electron energy loss spectroscopy or synchrotron x-ray powder diffraction. The improved densification of both the Co-doped and Mn-doped materials was believed to be related to an increased rate of lattice and grain boundary cation diffusion, associated with the segregation of the transition metal dopant to the grain boundary. In both cases the onset of rapid densification was correlated with the reduction of the transition metal cation leading to an increase in cerium interstitials, which are suggested to be the defects responsible for cerium diffusion. The inhibiting effects of Cr-addition were similarly related to changes in the defect chemistry, with the Cr ions creating a blocking effect that hindered the dominant grain boundary pathway for cation diffusion. The effects of these dopants on the electrical conductivity of CGO were examined using a combination of AC impedance spectroscopy and Hebb-Wagner polarisation measurements. Whilst Co-doping was found to enhance the specific grain boundary conductivity of CGO, the addition of either Cr or Mn resulted in an approximate 2 orders of magnitude decrease, even at dopant concentrations as low as 100 ppm. Despite these differences in ionic conductivity, both Co and Cr-doping were found to significantly enhance the electronic contribution to the conductivity along the boundaries, particularly within the p-type regime. The modified electrical behaviour was related to the formation of a continuous, transition metal-enriched grain boundary pathway and a change in the driving force for grain boundary Gd segregation, leading to a depletion of oxygen vacancies within the space charge regions and the consequent reduction of oxygen transport across the boundaries. The effects of this segregation were finally examined with mono-layer sensitivity using low energy ion scattering incorporating a novel method of self-standardisation. These analyses provided strong support for the conductivity mechanisms previously outlined.

Glass is used for the vitrification of high level waste that results from the reprocessing of spent nuclear fuel. A better understanding of the structure of vitrified wastes may lead to insights into the observed compositional flexibility. It is also the starting point for studies of the self-irradiation behaviour of glasses under long-term repository conditions. Appropriate models need to be employed for the study of glasses when using molecular dynamics. The nature of nuclear waste necessitates an accurate structure prediction for a range of compositions and parameters. To this end, the suitability of established potential sets have been compared. The established potential models were used to investigate the structure of zinc containing sodium silicate glass. Once validated, this structure was used to investigate structural changes observed during simulated self-irradiation, where significant changes were observed on the atomic scale. This will provide the basis for further studies of radiation damage, glass-crystal interfaces and damage across glass-crystal interfaces. In order to further enhance the understanding of potential models, a novel glass of composition LiAlF4 has been successfully described, and may become relevant in the future as a thin film coating in Li-ion batteries.

This thesis reports what is believed to be a new approach to the analysis of the spiral (clock-type) spring based on a re-thinking of the fundamental equations. Detailed examination of this type of spring has led to the discovery that the free spiral form approximates to a logarithmic spiral. Methods of examining the free spiral form are described and what are thought to be unique methods ·of determining its equation are presented. Knowledge of the spiral equation enables the moment-rotation characteristic to be constructed which is then compared with experimental results obtained on a testing machine designed by the author. This machine allows measurements of torque to be obtained without introducing machine friction. It has been designed to allovl autographiC recordings to be made of the spring test. Prediction of the spiral equation from consideration of the elastic-plastic behaviour of an idealised material has been achieved and charts have been produced which will facilitate this prediction. The relationship between the back-tension during winding and the free spiral form has also been investigated. A further research programme has been outlined which, together with the present findings, should lead to a complete understanding of the mechanics of the spiral-spring forming process however performed.

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The aim of this work was to develop oxide fuel cell (SOFC) cathodes made from (LaNiO3)nLaO Ruddlesden-Popper (R-P) phases, and to investigate novel in situ characterisation techniques for SOFC cathodes. Cathodes were developed from La2NiO4+δ (L2N1) and La4Ni3O10-δ (L4N3), R-P phases known to have attractive conductivities at SOFC temperatures. These phases were shown to be chemically stable, both with each other and with the common electrolyte material La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM). LSGM-supported symmetrical cells were fabricated with electrodes of single phase L2N1 and L4N3, and a range of L2N1+L4N3 composites. The performance of these was tested from 500 – 700 °C with the composites giving the lowest area-specific resistance (ASR); a 50:50 wt.% L2N1:L4N3 composition being optimal. Functionally graded electrodes were developed consisting of a thin compact L2N1 layer deposited onto the LSGM, topped by a thicker porous L2N1+L4N3 composite layer, completed by a thin porous L4N3 current collector. These gave a lower ASR than the ungraded electrodes. Using a 50:50 composite was optimal with ASRs of 15.59, 2.29, and 0.53 Ωcm2 at 500, 600, and 700 °C respectively; amongst the best-in-class for electrodes made from this type of material. X-ray absorption near-edge spectroscopy was chosen as a method to gain in situ information on the redox chemistry of elements within SOFC materials. Initial studies were carried out on powder samples of L2N1 and L4N3; the nickel oxidation state in these was found to reduce on heating to SOFC operating temperatures. Bespoke equipment was developed to enable such studies to be carried out on symmetrical cells under polarisation and with simultaneous AC impedance spectroscopy. The bulk nickel redox chemistry was correlated with the changing concentration of ionic charge carriers in the materials, and was found to be dominated by thermal effects. These techniques were then used to explore in situ chromium poisoning of state-of-the-art perovskite cathodes. The surface chemistry of SOFC materials is key to performance. Low-energy ion scattering was used to find the composition of the outer monolayer for the entire (LaNiO3)nLaO R-P series; lanthanum termination was found for each phase.