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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 Characterizing excited state transport and charge carrier dynamics in lead halide perovskites(Montana State University - Bozeman, College of Letters & Science, 2020) Hickey, Casey Lynn; Chairperson, Graduate Committee: Erik Grumstrup; Andrew H. Hill, Eric S. Massaro and Erik M. Grumstrup were co-authors of the article, 'Ultrafast excited-state transport and decay dynamics in cesium lead mixed halide perovskites' in the journal 'ACS energy letters' which is contained within this dissertation.; Andrew H. Hill and Erik M. Grumstrup were co-authors of the article, 'Screening links transport and recombination mechanisms in lead halide perovskites' in the journal 'The journal of physical chemistry C' which is contained within this dissertation.; Erik M. Grumstrup was a co-author of the article, 'Direct correlation of charge carrier transport to local crystal quality in lead halide perovskites' submitted to the journal 'Nano letters' which is contained within this dissertation.; Erik M. Grumstrup was a co-author of the article, 'A reduced artifact approach for determining diffusion coefficients in time-resolved microscopy' submitted to the journal 'The journal of physical chemistry C' which is contained within this dissertation.Understanding fundamental processes which drive the behavior of photoexcited charge carriers is essential to the development of novel semiconducting materials. The studies presented in this work combine ultrafast microscopy with a novel data analysis technique to provide an in-depth characterization of the excited state transport and recombination dynamics which occur in a series of lead halide perovskites. An investigation of the impact halide composition has on recombination dynamics in CsPbI 2Br revealed that trap-mediated recombination dominates at low fluences, with Auger recombination becoming increasingly important as the excitation density increases. Additionally, the average diffusivity measured for CsPbI 2Br (DA = 0.27 cm2/s) is nearly 10x lower than that observed in MAPbI 3. Further, it was determined that the dielectric constants relevant to photoexcited charge carriers in CsPbBr3 and MAPbBr3 perovskites (11.5 and 13, respectively) are intermediate between the high and low frequency limits, and that halide chemistry plays an integral role in determining the screening ability of lead halide perovskites. By correlating charge carrier diffusivities to locally measured crystal quality, it was found that solution processing methods can cause subtle lattice defects which act to impede transport and risk going undetected by bulk measurement techniques. Finally, to improve upon the traditional method for extracting diffusivities from transport measurements, which relies on perfectly Gaussian point spread functions, a new method was developed which instead relies on a numerical convolution of the actual point spread function with the diffusion equation. Compared to the traditional Gaussian method, the numerical convolution method proved to more accurately determine the diffusion coefficient, especially in the case of an anomalous point spread function.Item Characterizing excited state dynamics and carrier transport in hybrid organic-inorganic lead halide perovskites via ultrafast microscopy(Montana State University - Bozeman, The Graduate School, 2018) Hill, Andrew Hinson; Chairperson, Graduate Committee: Erik Grumstrup; Kori E. Smyser, Casey L. Kennedy, Eric S. Massaro and Erik M. Grumstrup were co-authors of the article, 'Ultrafast microscopy of methylammonium lead iodide perovskite thin films: heterogeneity of excited state spatial and temporal evolution' which is contained within this thesis.; Kori E. Smyser, Casey L. Kennedy, Eric S. Massaro and Erik M. Grumstrup were co-authors of the article, 'Screened charge carrier transport in methylammonium lead iodide perovskite thin films' in the journal 'Journal of physical chemistry letters' which is contained within this thesis.; Casey L. Kennedy, Eric S. Massaro and Erik M. Grumstrup were co-authors of the article, 'Perovskite carrier transport: disentangling the impacts of effective mass and scattering time through microscopic optical detection' in the journal 'Journal of physical chemistry letters' which is contained within this thesis.; Casey L. Kennedy and Erik M. Grumstrup were co-authors of the article, 'Determining the effects of A-site cation substitution on the optical response and transport properties of lead tri-bromide perovskites' submitted to the journal 'Journal of physical chemistry letters' which is contained within this thesis.Lead tri-halide perovskites have recently emerged as cost-effective alternatives to silicon for use in photovoltaic devices. A large contributor to their reduced cost compared to silicon is the simple solution processed techniques employed in their fabrication. While these methods can produce effective photovoltaic devices, heterogeneity endemic to solution processing makes characterization of tri-halide perovskites a challenging task. Most spectroscopic techniques use large sample interrogation volumes which often results in the indiscriminate sampling of grain boundaries and other heterogeneities which impact the spectroscopic observable. To circumvent this issue, pump-probe microscopy is used to dramatically shrink the sample volume, reducing the contributions from chemical and morphological heterogeneities and providing a more accurate measure of the sample's inherent properties. This work begins with a study of the recombination and transport dynamics methylammonium lead tri-iodide (MAPbI 3) perovskite. After identifying the main recombination pathways and contributions to the transient signal, experimental focus is shifted to the transport properties of MAPbI 3. The key contributing factors to the high diffusivities reported in MAPbI 3 are found to be strong electron-phonon coupling and a high static dielectric constant which serves to screen carriers from interactions with charged defects and other carriers. Then the development a new all-optical method capable of uniquely determining the two fundamental parameters that govern carrier transport (the mean scattering time and optical mass of photogenerated carriers) is reported. This method was applied to a series of different perovskite materials including MAPbI 3, cesium lead bromide di-iodide (CsPbBrI 2), methylammonium lead tri-bromide (MAPbBr 3), formamidinium lead tri-bromide (FAPbBr 3), and cesium lead tri-bromide (CsPbBr 3). The results of these experiments have led to the characterization of the role each perovskite constituent (namely, the identity of the organic cation and the halide stoichiometry) plays in determining the transport properties of the resulting material. The work presented in this dissertation characterizes the transport properties of lead halide perovskites. Measurements collected across multiple discrete and highly crystalline domains of multiple perovskite species have helped establish a relationship between the functionality and the local structure of these materials. Additionally, the design and first application of a new methodology to disentangle the effects of mean scattering time and the photogenerated carrier mass on carrier transport is reported. This technique will not only continue to aid in the characterization of lead-halide perovskites but will likely also see use on a host of other material systems to advance understanding of carrier transport in a variety of materials.Item Magnetic properties of two copper (II) halide layered perovskites(Montana State University - Bozeman, College of Letters & Science, 1992) Sivron, Nava RabinerItem 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.Item Sr 2-x VMoO 6-Y double perovskites : a new generation of solid oxide fuel cell anodes(Montana State University - Bozeman, College of Letters & Science, 2013) Childs, Nicholas Brule; Chairperson, Graduate Committee: Richard J. Smith; Cameron Law, Richard Smith, Stephen Sofie, Camas Key, Michael Kopcyzk and Michael Lerch were co-authors of the article, 'Electronic current distribution calculation for a NI-YSZ solid oxide fuel cell anode' in the journal 'Fuel cells' which is contained within this thesis.Fuel cells are an attractive power source due to their ability to efficiently convert chemical energy stored in fuel directly into electricity. The ability of Solid Oxide Fuel Cells (SOFCs) to reform hydrocarbons at the anode provides for fuel flexibility, an advantage over other types of fuel cell technologies. The primary goals of this dissertation were to investigate the limitations of the currently used anode cermet material, synthesize a double perovskite material (Sr ₂₋xVMoO ₆₋y) without these limitations and investigate the electrical conduction properties of this mixed ionic and electronic conductor (MEIC) in a SOFC anode environment. The electronic current density limitation of a Ni-YSZ anode was determined through the development of a computer simulation and use of experimental data. The electronic current density distribution for nickel particles in a Ni-YSZ anode was calculated via a Monte-Carlo percolation model. Experiments were performed to determine the failure current densities of thin nickel wires in a SOFC anode environment. The results show a current density limitation of Ni-YSZ anodes that is not expected with MEIC anodes. A MEIC anode material, Sr ₂₋xVMoO ₆₋y, was synthesized and characterized using a variety of techniques. The expected MEIC nature of this perovskite material eliminates a potential anode limitation, while adding other benefits over Ni-YSZ. X-ray diffraction (XRD) was used to verify crystal structure. In contrast to the trace amounts of secondary insulating phases found through XRD, XPS shows a high percentage (85-90%) of these secondary phases at the surface. The electrical conductivity of Sr ₂₋xVMoO ₆₋y was found to exceed that reported for Ni-YSZ anodes in a typical SOFC anode environment. Polycrystalline Sr 1.9VMoO ₆₋y'' samples exhibited higher electrical conductivity than that reported for SrMoO ₃ polycrystalline samples, making it a candidate for being the highest electrical conducting oxide known. These conduction values were only measured after specific thermal treatments in a reducing atmosphere. These treatments reduced secondary surface phases, Sr ₃V ₂O ₈ and SrMoO ₄, into their more conducting counterparts, SrVO ₃ and SrMoO ₃. Vanadium and molybdenum valence state XPS fitting parameters for primary and secondary phases are reported.