UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    CHARACTERIZING THE DURATION, PERIODICITY AND CHEMICAL IMPACT OF FLUID TRANSPORT IN THE SUBDUCTING SLAB: INSIGHTS FROM ISOTOPE GEOCHEMISTRY OF HIGH-PRESSURE METAMORPHOSED OCEANIC CRUST
    (2021) Hoover, William Floyd; Penniston-Dorland, Sarah C; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Subduction zones are key loci of geochemical cycling and natural hazards on Earth including large earthquakes and explosive volcanic eruptions. Fluids produced during subduction are thought to play a role in all these processes, however, many aspects of fluid transport in subduction zones remain enigmatic. In this dissertation, three types of fluid-related features are examined: 1) an eclogite-facies vein and 2) an eclogite- facies shear zone block and metasomatic rind, both from the Monviso Ophiolite (Western Alps), and 3) two amphibolite-facies mélange blocks and rinds from the Catalina Schist (CA). The mechanisms, episodicity and duration of fluid transport associated with these fluid pathways are investigated with bulk and in situ Li isotope geochemistry, in situ Sr isotope and trace element geochemistry, and quantitative transport modeling. In the eclogite-facies vein, evidence for five distinct locally-derived fluid compositions suggests a complex process of fluid-rock interaction. The unusual geometry of alteration features in the host rock suggests that initial host rock heterogeneity led to the development of reactive porosity channels. A method for in situ measurement of Li isotopes in garnet by secondary ion mass spectrometry is developed to explore the relative chronology of fluid rock interaction preserved in mineral zoning. The equivalence of natural garnet and garnet-like glass reference materials is demonstrated and a correction procedure for instrumental mass fractionation due to MnO and FeO is proposed. The resulting method is highly adaptable and attains 2-4‰ precision at the 20-μm-scale. Application of this method to garnet from the eclogite-facies shear zone block and rind reveals negative ?7Li excursions to values as low as -9‰ that record fluid-driven Li diffusion and rapid garnet growth. Multiple negative excursions within a single garnet require at least four episodes of fluid infiltration in the shear zone. Lastly, the first fluid transport durations for the subduction interface are obtained by inverting Li isotopes profiles from the amphibolite-facies mélange blocks and rinds using an advection-diffusion model. Uniform durations of ~60 years for metasedimentary rock-derived fluid flow near peak metamorphic conditions suggest fluid infiltration was pervasive and episodic, with earlier episodes erased by the expansion of rinds into blocks.
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    Ultrathin Materials for Advanced Energy Storage
    (2020) Hitz, Emily Michelle; Hu, Liangbing; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The demand for batteries that can meet the high energy density and reliability needs of the future is ever growing and drives current research trends in the battery field toward the development of practical metallic Li anodes. Overcoming the difficult rechargeability and safety obstacles that affected the first-generation lithium-ion batteries in decades past has required diligent research and introduced of a host of new material systems, including solid-state inorganic electrolytes. Solid-state electrolytes represent a fundamental departure from conventional liquid-electrolyte lithium-ion batteries and offer a path toward versatile and high-energy-density energy storage. Inorganic solid-state electrolytes have still faced challenges, such as unfavorable interface characteristics with electrode materials and low ionic conductivity compared to liquid electrolytes, but recent advancements have helped to overcome these obstacles and position solid-state electrolytes as promising candidates for use in state-of-the-art batteries. To achieve widespread adoption of solid-state electrolytes, however, prevailing issues like Li dendrite formation and subsequent electrical shorting must be understood and solved. Based on research that suggests a dependence of dendrite formation on the electronic conductivity of garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZO-Ta) solid electrolyte, I first investigate a thin, conformal layer of electronic-insulating, ion-conducting lithium phosphorus oxynitride (LiPON) deposited at the interface between garnet-type electrolyte and a metallic Li alloy anode. Using atomic layer deposition to ensure continuity of the LiPON layer across the garnet LLZO-Ta surface, I fabricate Li-Li symmetric cells that achieve long cycle life free of dendrites. After demonstrating the merits of a thin, electronically insulating layer applied at the interface between Li metal and LLZO-Ta, I probe into the relationship between the ionic and electronic conductivity of solid-state electrolytes with the goal of providing guidance on the rational design of dendrite-free solid-state electrolytes. Toward this aim, I consider an electronic-conductivity-modulated LLZO-Ta electrolyte matrix with LiPON coatings of varying thickness. With support from literature, I also explore the implications of an electron-blocking, ion-conducting layer in full-cell batteries, drawing conclusions about their potential use at the cathode-electrolyte interface. The impact of ion-conducting, electron-blocking thin surface coatings for Li dendrite inhibition in solid-state electrolytes is far-reaching and provides a reliable strategy for high-performance solid-state batteries.