Materials Science & Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2792
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Item Improving the performance of solid polymer electrolytes for lithium batteries via plasticization with aqueous salt or ionic liquid(2019) Widstrom, Matthew; Kofinas, Peter; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this dissertation is to investigate and enable polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) for lithium batteries. Specifically, two different strategies to plasticize the PEO matrix for improving ion transport are explored. PEO has a propensity to crystallize below 60C, rendering ion motion too slow to be commercially competitive and constituting one of the main challenges of utilizing PEO SPEs as an alternative to organic liquid electrolytes. ILSPEs incorporating ionic liquids (ILs) were fabricated by blending PEO, IL, and corresponding lithium salt followed by hot-pressing the mixture into a homogenous film. Aqueous SPEs (ASPEs) were fabricated by blending a highly concentrated solution of lithium salt in water (aqueous salt) with PEO followed by hot-pressing in a similar manner. Thermal analysis and electrochemical characterization were carried out for both classes of SPEs to assess their suitability as electrolytes and to optimize their composition for performance. Additionally, engineering the interface between the SPE and electrodes remains challenging and is critical for achieving good cycling performance. Multiple approaches for quality interface creation are proposed and carried out. Optimized ILSPE compositions show resistance to oxidation and were able to achieve room temperature conductivity of 0.96 mS/cm at room temperature, a value suitable for commercial application, as well as good rate performance at room temperature cycling in Li/ ILSPE/ lithium iron phosphate configuration. ASPE compositions exhibit conductivities between 0.68 and 1.75mS/cm at room temperature, with proof-of-concept cycling in a LTO/ ASPE/ LMO configuration.Item The Effect of Laser Shock Peening on Dislocation Morphology and Microstructural Evolution of AA5083-H116(2019) Tsao, Alice Uanchian; Ankem, Sreeramamurthy; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The AA5083-H116 aluminum alloys (Al-4.7Mg-0.62Mn-0.29Fe-0.15Si-0.099Cr-0.094Zn-0.036Cu-0.018Ti-0.086Other) are lightweight structural materials for marine applications. Due to the high magnesium content (>3wt.%), the sensitization of Al3Mg2 β-phase and susceptibility for intergranular stress corrosion cracking (IGSCC) in AA5083-H116 significantly increases under thermal exposure. The effects of laser-shock peening (LSP) on the kinetics of β-phase were studied via accelerated sensitization heat treatments between 70-175℃ for times between 5-3,600 hours. Optical microscopy, transmission electron microscopy (TEM), and finite element method (FEM) modeling were utilized to study the effect of LSP on AA5083-H116 microstructural evolution, dislocation morphology, and stress-strain distribution. FEM results showed LSP induces plastic compressive deformation near the surface. TEM observations confirmed the models, showing dislocation density increased by a factor of ~4.7, with residual tensile stresses throughout the thickness. The kinetics of β-phase precipitation and coarsening were not impacted by LSP; however, it is recommended that its influence on IGSCC should be investigated further.Item Superconducting Properties of the NbN and TiN alloy system.(2019) Santos-Cotto, Abimael; Richardson, Christopher J.K.; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The field of quantum computation has advanced greatly in the recent years, with materials being tuned to address issues like qubit lifetime, and coherence time. Superconducting qubits based on Josephson Junctions are a promising approach for improved qubit design, yet they are made with polycrystalline and amorphous materials. Transition metal nitrides, like TiN and NbN, offer good chemical and mechanical properties as well as the possibility of a lattice matched junction, with AlN as the insulating layer. We have characterized MBE grown NbxTi1-xN films (with x = 0, 0.45, and 0.78) and a Nb2N film by XRD and AFM. This thesis will focus on the superconducting properties: critical temperature (Tc), superconducting transition width (ΔTc), and critical field (Hc). Two methods have been used: four-point probe DC measurements in an adiabatic demagnetization refrigerator (ADR) were used for Tc and ΔTc measurements, and a magnetic properties measurement system (MPMS) which employs a SQUID magnetometer was employed for Tc and Hc measurements. Values of Tc ranged from 4.2 K for TiN to 15.2 K for the x= 0.45 film, and 14.8 for x=0.78, while the Nb2N had Tc of 9.9 K, as found by DC measurements. These values agreed with those found by MPMS. The films’ critical fields were found to be ~69.6 Oe for the TiN film and ~250 Oe for x=0.78. These results start to demonstrate the trends of the superconducting properties of alloyed NbxTi1-xN superconductors.Item First Principles Computational Design of Solid Ionic Conductors through Ion Substitution(2019) Bai, Qiang; Mo, Yifei; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid ionic conductors are key components of energy storage and conversion devices. To achieve high efficiency in these energy devices, solid ionic conductors should demonstrate high ionic or electronic conductivity. While pristine materials often suffer from poor conductivity, substituting ions in materials can tailor their electronic and ionic transport to fulfill requirements of transport properties in energy devices. In this dissertation, I applied first-principles computational techniques to elucidate the effect of ion substitution on electronic and ionic transport properties of solid materials. Therefore, three representative materials SrCeO3, La2-x-ySrx+yLiH1-x+yO3-y, and Li6KTaO6 are investigated as model systems to elucidate how ion substitution can affect the transport of electron, anion, and cation, respectively. I studied SrCeO3 as a model material to uncover the effects of B-site dopants on electronic transport. Based on theoretical calculations, I confirmed a polaron mechanism, including polaron formation and hopping, contributed to the electronic conductivity of SrCeO3. I found different dopants exhibit distinct capabilities for localizing electron polarons, and therefore result in different electronic conductivities in doped SrCeO3. The study demonstrated the capabilities of first principles computation to design new materials with desired polaron formation and migration. I studied La2-x-ySrx+yLiH1-x+yO3-y oxyhydrides as a model material to investigate H- diffusion mechanism in a mixed anion system and its relationship with the cation substitution of Sr2+ to La3+. I found the substitution of Sr2+ to La3+ can alter the H- diffusion mechanism from 2D to 3D pathways. Increasing H- vacancies through Sr2+ to La3+ substitution can also expedite the H- conductivity of the oxyhydrides. Based on the new understanding, a number of promising dopants in Sr2LiH3O were predicted to enhance H- transport. Fast Li-ion conductor materials as solid electrolytes are crucial for the development of all-solid-state Li-ion batteries. I systematically studied Li+ diffusion mechanisms in Li6KTaO6 predicted by our computational study. I found that different carrier defects such as Li vacancies or interstitials can induce distinct Li+ transport mechanisms. In addition, I developed a computational workflow to predict a wide range of materials in a prototype structure. By employing the workflow, I computationally predicted a group of Li superionic conductors with good stabilities by substituting the Li6KTaO6 structure.Item NEXT GENERATION ANODES FOR LITHIUM ION AND LITHIUM METAL BATTERIES(2019) Pastel, Glenn; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Engineering of specific battery components can yield incremental gains in performance, but sustained advancements are derived from an understanding of charge transfer, interphase formation, and ion storage in the system. In this dissertation, the next generation of lithium-ion and alkali metal anodes are integrated with promising flame retardant electrolyte systems for safe and energy-dense portable storage devices. The intent of this research is to bring safe lithium ion batteries to the market without compromising performance and, more specifically, volumetric energy density. The first part of this dissertation describes the invention and optimization of a silicon-based additive which employs a solution-based process to functionalize silicon nanoparticle precursors. The additive is thoroughly characterized by chemical and electrochemical methods and the electrolyte interphase is improved by the attachment of partially reduced graphene oxide and sacrificial additive species. The design principles developed for the silicon-based system deviate significantly from those used for other conventional intercalation and host electrodes. As a result, in the second part of this dissertation, three chemically separable electrolyte systems, selected for their flame retardant properties, are individually investigated and tailored for energy-dense pouch cells. The bulk transport and interfacial properties of each electrolyte system are adapted to meet the industry standards of portable electronic devices. Insights into the preferred species for stable solid electrolyte interphase formation are discussed with an emphasis on the impact of fluorinated solvents and sacrificial additives. In the last part of this dissertation, alkali metal hosts are also proposed for chemistries beyond lithium ion. Novel synthesis methods including rapid joule heating are explored to form the innovative host architectures which greatly mitigate the coulombic inefficiency of metal stripping and plating in half and full cell configurations. The design principles outlined in this dissertation reveal how to successfully engineer the charge transfer, interphase formation, and ion storage of high capacity electrodes with safe electrolyte for state-of-the-art portable energy storage devices.Item Radiation Effects in Diamond Substrates and Transistors(2019) Thapa, Aayush; Christou, Aris; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Diamond and diamond devices are potentially radiation damage resistant due to diamond’s wide bandgap and high displacement energy per atom. Conducting channels in diamond—necessary for the realization of field effect transistors (FETs)—are based on hydrogen-terminated surfaces or buried implanted acceptors (delta doping). The present thesis investigates the susceptibility of these channels to either ionizing or non-ionizing radiation. Gamma radiation tolerances of H-terminated based FETs at low (≤100 krad) and high doses up to 26 Mrad, and proton radiation tolerance of H-terminated and delta doped substrates at 152 keV and fluences of 1.02 x1012 cm-2 are studied. For gamma radiation, we report a decrease in drain current and threshold voltage for low dose but increase in both at high dose. And for proton radiation, we report a change in activation energy for conductivity, an increase in resistivity, and a decrease in both mobility and carrier concentration.Item HIGH TEMPERATURE PROCESSED NANOSTRUCTURES FOR EMERGING ELECTROCHEMICAL DEVICES(2019) Xie, Hua; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ancients exploited fire to keep warm, but temperature embodies more than just warm and cold. Researchers employ high temperatures as a useful tool to develop novel materials. Many reactions require high energy input at the very beginning or during the whole synthesis process. High temperature synthesis is an effective approach to synthesize new materials or to achieve designed phase structures. This approach can be operated under air, a reducing atmosphere, or high vacuum, which are suitable for various applications and are widely used in chemical decomposition and compounding, powder sintering and densifying, as well as nanocrystal growth. In this work, high temperature techniques are applied to two distinct emerging energy-related electrochemical systems, improving the key component material properties for advanced applications. In the first part of the work, a thermal shock approach is employed to synthesize carbon-based composite materials and platinum-group metal (PGM)-free electrocatalysts for oxygen reduction reactions in fuel cells. Specifically, this work has focused on the nanostructure design of graphene/metal nanoparticles to enhance their chemical stability and electrochemical durability during reactions. In addition to the systematic characterization, detailed electrochemical performance evaluations were carried out to get a further understanding of the mechanism, which allows for better materials nanoengineering and amelioration in the resulting devices. The second primary research topic in this dissertation focuses on the high temperature synthesis and post-treatment of high performance Garnet-type solid state electrolytes, which are a promising candidate to replace conventional flammable liquid electrolytes for lithium batteries. A melted lithium-alloying approach is applied to improve the interfacial wettability and stability between the lithium metal anode and Garnet solid-state electrolyte. Thermal shock post-treatment on the Garnet electrolyte is demonstrated to significantly eliminate the impurities and improve the electrochemical properties, such as ionic conductivity. Sol-gel and template methods are carried out to demonstrate a fast synthesis approach to achieve hybrid Garnet electrolytes with excellent flexibility and good performance. Additional investigation includes analysis of the theoretical fracture mechanics of electrolyte as determined by dimensionality. A mechanics-guided strategy is employed to design a composite solid-state electrolyte with superb flexibility.Item Characterizing the effect of atomic layer deposited coatings for the prevention of glass alteration in museum collections(2019) Hiebert, Miriam; Phaneuf, Raymond J; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Glass alteration in museum collections poses a serious problem for museum conservators and collections managers. There are currently few options available to slow or stop the progression of glass alteration. This thesis work has focused on assessing the potential use of atomic layer deposited (ALD) amorphous metal oxide coatings on glass as a potential solution to this problem. A modified ASTM accelerated aging method was used to age the glass samples within a time frame that could be reasonably studied, and the spatially-averaged alteration responses of the glass types chosen for this thesis were determined. The effect of applied ALD coatings on the alteration experienced by glass samples that had been subjected to accelerated aging was assessed. It was found that while TiO2 ALD films did not have a significant effect on the degree of alteration experienced, Al2O3 ALD coatings resulted in a significant decrease in the alteration response measured. The success of these coatings was limited, however, by the presence of coating defects, which expand significantly on the surface of the glass samples as a result of the accelerated aging method used. These defects stem from both the formation of pinholes in the coating during the ALD process, and cracking or buckling of the coatings due to mismatches in the coefficients of thermal expansion between the glass and the coating. Methods of mitigation for the formation of these defects and resulting coating loss were investigated. In addition to the efficacy of the ALD coatings, the appropriateness of this method for the treatment of museum objects was assessed. This included investigations of the impact on the appearance of the object imparted by the coatings. Al2O3 ALD coatings were found to have a minimal effect on the perceived color of the glass samples. In addition, the reversibility of the treatment was examined, and it was found that Al2O3 ALD are able to be removed quickly and safely from glass sample surfaces using mild alkali etchant solutions.Item MULTI-LAYERED, VARIABLE POROSITY SOLID- STATE LITHIUM-ION ELECTROLYTES: RELATIONSHIP BETWEEN MICROSTRUCTURE AND LITHIUM-ION BATTERY PERFORMANCE(2019) Hamann, Tanner; Wachsman, Eric; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global drive to create safer, higher capacity energy storage devices is increasingly focused on the relationship between the microstructures of electrochemically- active materials and overall battery performance. The advent of solid-state electrolytes with multi-layered, variable porosity microstructures opens new avenues to creating the next generation of rechargeable batteries, while creating new challenges for device integration and operation. In this dissertation, microstructures of solid-state Li-ion conducting electrolytes were characterized to identify the primary limiting factors on electrolyte performance and identify structural changes to improve porous electrolyte performance in dense-porous bilayer systems. LLZO-based garnet electrolytes were fabricated with varied porosity and characterized using 3D Focused Ion Beam (FIB) Tomography, enabling digital reconstructions of the underlying 3D microstructures. Ion transport through the microstructures was analyzed using M-factors, which identified garnet volume fraction and bottlenecks as primary limiters on effective conductivity, followed by geometric tortuosity. Notably, a template-based porous microstructure displayed a low tortuosity plane and a high tortuosity direction, as opposed to the more homogenous tape-cast porous microstructures. To evaluate the performance of these microstructures in Li symmetric cells, dense-porous bilayers were digitally constructed using the FIB Tomography microstructures as porous layers with fully infiltrated Li-metal electrodes, and equilibrium electric potentials were simulated. The bilayers had area-specific resistance (ASR) values similar to the ASR value of the dense layer alone. The bilayer ASR also decreased as porous layer porosity increased, due to ion transport occurring primarily through the dense layer-electrode interface and higher porosity creating higher interfacial area. Artificial bilayers were created with porous layers composed of columns for a range of column diameters/particle sizes, porous layer porosities, and porous layer thicknesses. The bilayer ASR decreased with increasing porosity and decreasing column diameter, similar to the FIB Tomography bilayers. However, bilayer ASR dramatically increased when only partially infiltrated with electrodes, and instead increased with increasing porosity and decreasing column diameter. The simulation results showed that fabricating solid-state bilayer symmetric cells with low ASR required high porosity porous microstructures with small particle sizes, and electrodes completely infiltrated to the dense layer.Item ATOMIC LAYER DEPOSITION OF LEAD ZIRCONATE-TITANATE AND OTHER LEAD-BASED PEROVSKITES(2019) Strnad, Nicholas Anthony; Phaneuf, Raymond J; Polcawich, Ronald G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lead-based perovskites, especially lead zirconate-titanate (PbZrxTi1-xO3, or PZT), have been of great technological interest since they were discovered in the early 1950s to exhibit large electronic polarization. Atomic layer deposition (ALD) is a thin-film growth technique capable of uniformly coating high aspect-ratio structures due to the self-limited nature of the precursor chemisorption steps in the deposition sequence. In this thesis, a suite of related processes to grow lead-based perovskites by ALD are presented. First, a new process to grow ferroelectric lead titanate (PbTiO3, or PTO) by ALD using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) [Pb(DMAMP)2] and tetrakis dimethylamino titanium [TDMAT] as the lead and titanium cation precursors, respectively, is discussed. A 360-nm thick PTO film grown by ALD displayed a maximum polarization of 48 µC/cm2 and remanent polarization of ±30 µC/cm2. Second, a new process (similar to the ALD PTO process) to grow PZT by ALD is demonstrated by partial substitution of TDMAT with either tetrakis dimethylamino zirconium or zirconium tert-butoxide. The 200 nm-thick ALD PZT films exhibited a maximum polarization of 50 µC/cm2 and zero-field dielectric constant of 545 with leakage current density < 0.7 µA/cm2. Third, a new ALD process for antiferroelectric lead hafnate (PbHfO3, or PHO) is presented along with electrical characterization showing a field-induced antiferroelectric to ferroelectric phase transition with applications for capacitive energy storage. Finally, ALD lead hafnate-titanate (PbHfxTi1-xO3, or PHT), considered to be an isomorph of PZT, is demonstrated by combining the process for PTO and PHO. The thin-film PHT grown by ALD is shown to have electronic properties that rival PZT grown at compositions near the morphotropic phase boundary (MPB). The processes for both ALD PZT and PHT are shown to yield films with promising properties for microelectromechanical systems (MEMS) actuators and may help to dramatically increase the areal work density of such devices.