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Item Multi-component oxide powder processing dynamics & synergy towards multi-functionality(Montana State University - Bozeman, College of Engineering, 2022) Heywood, Stephen Kevin; Chairperson, Graduate Committee: Stephen W. Sofie; This is a manuscript style paper that includes co-authored chapters.Multi-component or multi-cation ceramic oxides are particularly sensitive to processing-properties variation, in which a single defined chemical stoichiometry can embody dramatic variability in measured properties simply through the steps of synthesis and processing to reach the desired form. Hence, the tailoring of complex oxides is often convoluted by chemical doping and changes in stoichiometry when the influence of processing is not understood. Mixed conducting, multi-valent double perovskite Sr 2-x V Mo O 6-delta (SVMO) shows extraordinary electrical conductivity relative to comparable double perovskites. The technical hurdles of synthesizing and processing bulk powders of SVMO to optimize studies of fundamental electrical transport mechanisms otherwise convoluted by porosity in prior literature were overcome. The basis of various synthesis conditions via rapid microwave assisted sol-gel synthesis were discerned for their contribution to either open porosity of SVMO or enhanced densification. Enhanced resistance to particle coarsening under reducing contrast to inert atmosphere and a means to generate electrical percolation via solid-solution stability of SVMO were two key discoveries among fundamental breakthroughs understanding particle consolidation behaviors. It was discovered that SVMO's elastic modulus was well in excess of other oxide materials, approaching 300 GPa and in correspondence with the mixed V/Mo valency system provides an explanation for low thermal diffusion during sintering. The advanced solid lithium conducting garnet Li 6.25 La 3 Zr 2 Al 0.25 O 12 (LLZO) demonstrates high ionic conductivity for all solid-state batteries, however, it must be paired with an active cathode and anode to enable high energy storage capacity. The study presented here identifies methods to process LLZO materials into dense and porous constituents to satisfy the design architecture of a solid-state battery emphasizing the sensitivity of LLZO performance to lithium content and the desired cubic phase. The aim was to calibrate synthesis techniques towards minimizing sensitivity to thermal processing that contributes towards lithium loss. Studies of sintering optimization and excess lithium content in conjunction with novel freeze based tape casting methods to generate low tortuosity pores were explored. Development of these novel microstructures represents a backbone of processing methodology necessary to incorporate multivalent double perovskites in fuel-electrolysis cells and improve solid state lithium battery technologies.Item Investigation of multivalent double perovskites as electrodes for high temperature energy conversion(Montana State University - Bozeman, College of Engineering, 2012) Weisenstein, Adam John; Chairperson, Graduate Committee: Stephen W. Sofie; Nick Childs, Roberta Amendola, David Driscoll, Stephen Sofie, Paul Gannon and Richard Smith were co-authors of the article, 'Processing and characterization of Sr 2-xVMoO 6-delta double perovskites' submitted to the journal 'Journal of materials chemistry and physics' which is contained within this thesis.; Stephen Sofie was a co-author of the article, 'Fuel electrode performance of Sr 2VMoO 6 double perovskites' which is contained within this thesis.Solid Oxide Fuel Cells (SOFCs) are direct energy conversion devices that have demonstrated viability due to the associated high efficiencies, utilization of transition metal catalyst, and their unique fuel flexibility, which allows the use of dirty hydrocarbons. These high temperature systems typically utilize fuel electrodes composed of a ceramic/metal (cermet) composite that is comprised of nickel and yittria-stabilized zirconia (YSZ). While these systems have demonstrated performance potential due to the catalysis and electrical conductivity of nickel metal, a key shortcoming is the poor thermal stability of nickel metal at operating temperatures of 750-1000°C, for which increased temperature enhances performance. Nickel metal particle networks as well as other transition metal catalysts operating at high temperatures coarsen or agglomerate resulting in the loss of continuous electronic pathways. To address these challenges, new materials have been sought after to replace the mixed metal and ceramic two-phase Ni/YSZ fuel electrode. One proposed solution is to utilize a single phase Mixed Ionic Electronic Conductor (MIEC) to replace the traditional cermet structure. In this study, the analysis and characterization of the processing and sintering of Sr 2-xVMoO 6-delta perovskites, where x=0.0, 0.1 and 0.2, was investigated. Sr 2-xVMoO 6-delta substrates were sintered in a reducing atmosphere (5%H 2 95%N 2) and the x-ray diffraction patterns indicate that the double perovskite is the primary phase for Sr 2-xVMoO 6-delta pellets sintered at 1200°C and 1300°C for 20 hours. However, these pellets show a secondary phase of SrMoO 4-delta. X-ray photoelectron spectroscopy revealed a deficiency of vanadium on the pellet surfaces in which samples yielded surface vanadium concentrations of less than 5%. The vanadium inhomogeneity can be explained by the formation of the SrMoO 4-delta scheelite phase due to oxygen exposure on the surface of the pellets, which indicates inward vanadium migration to the bulk. Sr 2-xVMoO 6-delta pellets sintered at 1300°C showed very high conductivity, with Sr 1.9VMoO 6-delta exhibiting conductivity over 100,000S/cm at room temperature. The conductivity tests also indicate a semiconductor to metallic transition for all double perovskites related to the reduction of Mo6+ to Mo4+. Utilizing the double perovskites as fuel electrodes proved to be difficult, due to anion transport leading to secondary phases and thus delamination.