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This thesis extends our fundamental knowledge in the area of high oxidation state chemistry of xenon trioxide, XeO3. Oxygen coordination to the Xe(VI) atom of XeO3 was observed in its adducts with triphenylphosphine oxide, [(C6H5)3PO]2XeO3, dimethylsulfoxide, [(CH3)2SO]3(XeO3)2, pyridine-N-oxide, (C5H5NO)3(XeO3)2, and acetone, [(CH3)2CO]3XeO3. The crystalline adducts were characterized by low-temperature single-crystal X-ray diffraction and Raman spectroscopy. Unlike solid XeO3, which detonates when mechanically or thermally shocked, the solid [(C6H5)3PO]2XeO3, [(CH3)2SO]3(XeO3)2, and (C5H5NO)3(XeO3)2 adducts are insensitive to mechanical shock, but undergo deflagration when exposed to a flame. Both [(C6H5)3PO]2XeO3 and (C5H5NO)3(XeO3)2 are air-stable at room temperature. The xenon coordination sphere in [(C6H5)3PO]2XeO3 is a distorted square pyramid and provides the first example of a five-coordinate Xe center in a XeO3 adduct. The xenon coordination sphere of the remaining adducts are distorted octahedral comprised of three equivalent Xe---O secondary contacts that are approximately trans to the primary Xe–O bonds of XeO3. Hirshfeld surfaces of XeO3 and (C6H5)3PO in [(C6H5)3PO]2XeO3 show the adduct is well-isolated in its crystal structure and provide a visual representation of the secondary Xe---O bonding in this adduct. Crown ethers have been known for over 50 years, but no example of a complex between a noble-gas compound and a crown ether or another polydentate ligand had been reported. Xenon trioxide is shown to react with 15-crown-5 to form the kinetically stable (CH2CH2O)5XeO3 adduct which, in marked contrast with solid XeO3, does not detonate when mechanically shocked. The crystal structure shows that the five oxygen atoms of the crown ether are coordinated to the xenon atom of XeO3. The gas-phase Wiberg bond valences and indices and empirical bond valences indicate the Xe---Ocrown bonds are predominantly electrostatic, σ-hole, bonds. Mappings of the electrostatic potential (EP) onto the Hirshfeld surfaces of XeO3 and 15-crown-5 in (CH2CH2O)5XeO3 and a detailed examination of the molecular electrostatic potential surface (MEPS) of XeO3 and (CH2CH2O)5 reveal regions of negative EP on the oxygen atoms of (CH2CH2O)5 and regions of high positive EP on the xenon atom that are also consistent with σ-hole bonding. Reactions of crown ethers with HF acidified aqueous solutions of XeO3 at room-temperature yielded adducts of 12-crown-4, (CH2CH2O)4XeO3, and 18-crown-6, [(CH2CH2O)6XeO3∙2H2O]2∙HF, whereas slow cooling of a solution of XeO3 with 18-crown-6 in acetone yielded (CH2CH2O)6XeO3∙2H2O. The adducts (CH2CH2O)4XeO3 and (CH2CH2O)6XeO3∙2H2O are shock-insensitive whereas the former adduct is air-stable at room temperature. The low-temperature, single-crystal X-ray structures show the Xe atom of XeO3 coordinated to the oxygen atoms of the crown ether ring. Uncharacteristic xenon coordination numbers exceeding six (including the three primary bonds of XeO3) were observed for all crown ether adducts. Raman spectroscopy frequency shifts are consistent with complex formation and provided evidence for the 2,2,1-cryptand adduct of XeO3. Gas-phase Wiberg bond valences and indices and empirical solid-state bond valences confirmed the electrostatic nature of the Xe---O bonding interactions. Comparisons between the XeO3 and SbF3 18-crown-6, 15-crown-5, and 12-crown-4 complexes are made. Incorporation of xenon trioxide, XeO3, into inorganic polyatomic salts under ambient conditions has been observed in several mixed xenate salts; K[XeO3XO3] (X = Cl, Br), K2[XeO3SeO4]∙HF, K[(XeO3)nZO3] (Z = I, N), and M2[(XeO3)nCO3]∙xH2O (M = Na, K, Rb, Ba). Raman spectroscopy was used to identify the aforementioned compounds and K[XeO3ClO3], K[XeO3BrO3], K2[XeO3SeO4]∙HF, and Rb2[(XeO3)2CO3]∙2H2O were also characterized by low-temperature, single-crystal X-ray diffraction. The xenon atom of XeO3 is seven coordinate in K[XeO3ClO3] and six coordinate in all other compounds with Xe---O distances that are significantly less than the sum of the Xe and O van der Waals radii. These salts provide examples of XeO3 coordinated to inorganic compounds and may provide insights into the inclusion of xenon oxides in minerals. / Thesis / Master of Science (MSc)

Li-ion batteries (LIBs) have achieved remarkable success in electric vehicles (EVs), consumer electronics, grid energy storage, and other applications thanks to a wide range of electrode materials that meet the performance requirements of different application scenarios. Cathodes are an essential component of LIBs, which governs the performance of commercial LIBs. Layered transition metal oxide, i.e., LiNixCoyMn1-x-yO2 (NMC), is one family of cathodes that are widely applied in the prevailing commercial LIBs. With increasing demand for high energy density, the development of layered oxide cathodes is towards high Ni content because Ni redox couples majorly contribute to the battery capacity. Meanwhile, the battery community has been making tremendous efforts to eliminate Co in layered cathodes due to its high cost, high toxicity, and child labor issues during Co mining. However, these Ni-rich Co-free cathodes usually suffer from low electrochemical and structural stability. Several strategies are adopted to enhance the stability of Ni-rich Co-free cathodes, such as doping, coating, and synthesizing single crystal particles. However, the design principles and synthesis mechanisms of these approaches have not been fully understood. Herein, we design and synthesize stable Ni-rich and low/no-Co layered oxide cathodes by manipulating the chemical and structural properties of cathode particles. Our studies reveal the cathode formation mechanisms and shed light on the cathode design through complementary synchrotron microscopic and spectroscopic characterization methods. In Chapter 1, the motivation for LIB research is introduced from the perspective of its indispensable role in achieving carbon neutrality. We then comprehensively introduce the status of LIBs at present, including assessing their sustainability, worldwide supply chain and manufacturing, and cathode materials. Subsequently, we focus on the Co-free layered oxide cathodes and discuss their structure, limitations, and strategies to address the challenges. Finally, we discuss single crystal Ni-rich layered oxide cathodes and the challenges and strategies associated with their synthesis. In Chapter 2, we investigate the dopant redistribution, phase propagation, and local chemical changes of layered oxides at multiple length scales using a multielement-doped LiNi0.96Mg0.02Ti0.02O2 (Mg/Ti-LNO) as a model platform. We observed that dopants Mg and Ti diffuse from the surface to the bulk of cathode particles below 300 °C long before the formation of any layered phase, using a range of synchrotron spectroscopic and imaging diagnostic tools. After calcination, Ti is still enriched at the cathode particle surface, while Mg has a relatively uniform distribution throughout cathode particles. Our findings provide experimental guidance for manipulating the dopant distribution upon cathode synthesis. In Chapter 3, we synthesized Mn(OH)2-coated single crystal LiNiO2 (LNO) and used it as the platform to monitor the Mn redistribution and the structural and chemical evolution of the LNO cathode. We use in situ transmission X-ray microscopy (TXM) to track the Mn tomography inside the LNO particle and Ni oxidation state evolution at various temperatures below 700 °C. We further reveal chemical and structural changes induced by different extents of Mn diffusion at ensemble-averaged scale, which validates the results at the single particle scale. The ion diffusion behavior in the cathode is highly temperature dependent. Our study provides guidance for ion distribution manipulation during cathode modification. In Chapter 4, we successfully fabricated a surface passivation layer for NMC particles via a feasible quenching approach. A combination of bulk and surface structural characterization methods show the correlation of surface layer with bulk chemistry including valence state and charge distribution. Our design enables high interfacial stability and homogeneous charge distribution, impelling superior electrochemical performance of NMC cathode materials. This study provides insights into the cathode surface layer design for modifying other high-capacity cathodes in LIBs. In Chapter 5, we use statistical tools to identify the significance of multiple synthetic parameters in the molten salt synthesis of single crystal Ni-rich NMC cathodes. We also create a prediction model to forecast the performance of synthesized single crystal Ni-rich NMC cathodes from the input of synthetic parameters with relatively high prediction accuracy. Guided by the models, we synthesize single crystal LiNi0.9Co0.05Mn0.05O2 (SC-N90) with different particle sizes. We find large single crystals show worse capacity and cycle life than small single crystals especially at high current rates due to slower Li kinetics. However, large single crystal has higher thermal stability potentially because of smaller specific surface area. The findings of particle size effect on the performance provide insights into size engineering while developing next-generation single crystal Ni-rich NMC cathodes. The statistical and prediction models developed in this study can guide the molten salt synthesis of Ni rich cathodes and simplify the optimization process of synthetic parameters. Chapter 6 summarizes our efforts on the novel design and fundamental understanding of the state-of-the-art cathodes. We also provide our future perspectives for the development of LIBs. / Doctor of Philosophy / Lithium-ion batteries (LIBs) have been studied for decades and are widely applied in electronics and vehicles because of their high energy density and long lifetime. With the increasing demand for higher energy density, particularly in electric vehicles, the development of Ni-based layered oxide cathode materials has been focused on increasing the Ni content. Meanwhile, decreasing or eliminating Co has become a consensus due to its high cost, toxicity, and human rights issues during mining. Enhancing the stability of these Ni-rich and low/no-Co layered oxide cathodes is challenging yet crucial to their practical applications. Herein, we design and synthesize multiple Ni-rich and low/no-Co layered cathodes through ion distribution engineering and structure modification at various length scales. We also investigate the dopant redistribution, phase propagation, and local chemical changes during layered oxides cathode formation through a combination of complementary characterization methods at different length scales. In addition, we provide guidance for synthesis optimization by statistical correlations and performance prediction models with the input of synthetic conditions. Overall, this dissertation provides insights into the design and synthesis principles of Ni-rich low/no-Co layered oxide cathode, which can facilitate the transition to a sustainable future with next-generation LIBs.

A nearly stoichiometric, (1×1) Cr₂O₃ (101̲2) surface was prepared from a single crystal of α-Cr₂O₃. The five-coordinate cations exposed at the stoichiometric surface dissociatively adsorb molecular oxygen to form a (1×1), terminating chromyl (Cr=O) layer that is stable to >1100 K. TDS and AES were used to investigate the reactivity of the halo-alkanes CFCl₂CH₂Cl, CF₂ClCH₂Cl, CF₃CH₂Cl, and CF₂CH₂F, in addition to the halo-alkenes CFCl=CH₂ and CF₂=CH₂. The halo-alkanes CFCl₂CH₂Cl, CF₂ClCH₂Cl, and CF₃CH₂Cl undergo 1,2-dihalo elimination similar to the Zn-catalyzed dehalogenation of vicinal dihalides to form alkenes. Some acetylene is also formed. The halo-alkenes CFCl=CH₂ and CF₂=CH₂ decompose to yield acetylene. Halogen removed from the molecules remains bound to the surface following TDS experiments and eventually terminates the surface chemistry due to site blocking of the cations. Reactivity is directly related to the chlorine content of the molecules investigated. Only CFCl₂CH₂Cl was reactive on a chromyl-terminated surface. / Ph. D.

This research provides the first known procedure for cleanly and consistently reducing the diameter of single-crystal sapphire optical fiber (SCSF) below the limits of standard production methods, including the first production of subwavelength-diameter optical fiber (SDF) composed of single-crystal sapphire. The first known demonstration of an air-clad single crystal sapphire optical fiber demonstrating single-mode behavior is also presented, and the single-mode cutoff wavelength and diameter are determined. Theoretical models describing and predicting the optical behavior of low modal volume sapphire optical fibers are also presented. These models are built upon standard weakly-guiding optical fiber theory, which is found to be accurate once experimentally-determined properties of the SCSF are substituted for theoretical values. Reduced modal dispersion is also observed in the form of decreased laser pulse broadening in reduced-diameter SCSF. The improvements in spatial resolution for distributed sensing systems such as Raman distributed temperature sensing are also predicted based on the measured decrease in pulse duration. This research also provides an enhanced understanding of the etching behavior of sulfuric and phosphoric acids on sapphire surfaces, including the first reporting of etching rates and activation energies for a-plane sapphire surfaces. Morphological changes of sulfuric and phosphoric acids at and beyond the temperature ranges used in etching were also tested and discussed in detail, especially regarding their practical impact on observed etching behavior. The demonstration of LMV single-crystal sapphire optical fibers enables the adaptation of numerous sensing schemes requiring low modal volume or single-mode behavior to be utilized in extreme environments. / Ph. D.

Yes / Multi-ionizable compounds, such as dicarboxylic acids, offer the possibility of forming salts of drugs with multiple stoichiometries. Attempts to crystallize ciprofloxacin, a poorly water-soluble, amphoteric molecule with succinic acid (S) resulted in isolation of ciprofloxacin hemisuccinate (1:1) trihydrate (CHS-I) and ciprofloxacin succinate (2:1) tetrahydrate (CS-I). Anhydrous ciprofloxacin hemisuccinate (CHS-II) and anhydrous ciprofloxacin succinate (CS-II) were also obtained. It was also possible to obtain stoichiometrically equivalent amorphous salt forms, CHS-III and CS-III, by spray drying and milling, respectively, of the drug and acid. Anhydrous CHS and CS had melting points at ∼215 and ∼228 °C, while the glass transition temperatures of CHS-III and CS-III were ∼101 and ∼79 °C, respectively. Dynamic solubility studies revealed the metastable nature of CS-I in aqueous media, resulting in a transformation of CS-I to a mix of CHS-I and ciprofloxacin 1:3.7 hydrate, consistent with the phase diagram. CS-III was observed to dissolve noncongruently leading to high and sustainable drug solution concentrations in water at 25 and 37 °C, with the ciprofloxacin concentration of 58.8 ± 1.18 mg/mL after 1 h of the experiment at 37 °C. This work shows that crystalline salts with multiple stoichiometries and amorphous salts have diverse pharmaceutically relevant properties, including molecular, solid state, and solubility characteristics. / Solid State Pharmaceutical Cluster (SSPC), supported by Science Foundation Ireland under grant number 07/SRC/ B1158.

Pharmaceutical solids tend to exist in different physical forms termed as polymorphs. Issues about pharmaceutical systems are mainly concerned with the active ingredient's physico-chemical stability and bioavailability. The main aim of this study is to investigate the non-bonded interactions in pharmaceutical solids that govern the physical pharmaceutics performance of such materials and through the use of structural techniques and correlation of these results with crystal structural database to establish the presence of physical motifs in selected systems. Structural motifs were identified by the use of single crystal and crystal packing analysis on diverse range of pharma-relevant materials including chalcones, cryptolepines, biguanides and xanthines. These selected systems were validated using functional group and molecular analysis and correlating them to the Cambridge Structural Database. Crystallization studies are done on these selected systems as well as exploiting those using synthetic analogues. A total of 51 crystal structures were investigated including 16 new structure determinations. Addition synthesis of new xanthines to investigate novel intermolecular patterns was also undertaken. The understanding and exploitation of intermolecular interactions involving hydrogen bonds and coordination complexation during packing can be used in the design and synthesis of solid state molecular structures with desired physical and chemical properties.

The aim of this thesis was to improve the understanding of microstructure in single crystal ferroelectrics. This was achieved through macroscopic testing of Lead Magnesium Niobate – Lead Titanate (PMN-PT) and microscopic observations of Barium Titanate (BT) single crystals. Multi-axial polarization rotation tests on PMN-PT showed a gradual increase in the change in dielectric displacement due to ferroelectric switching as the electric field is applied at increasing angles to the initial polarization direction. A relatively high remnant polarization for loading angle near to 90° suggested that PMN-PT is more polarizable in certain directions. Strains measured in two directions, parallel to the electric field and perpendicular to the electric field, showed a noticeable variation on two opposite faces of the specimen suggesting an effect of local domain configurations on macroscopic behaviour. A micromechanical model gave an insight into the switching systems operating in the crystal during the polarization rotation test. Domain structure in BT was mapped using synchrotron X-ray reflection topography. By making use of the angular separation of the diffracted reflections and specimen rocking, different domain types could be unambiguously identified, along with the relative tilts between adjacent domains. Fine needle domains (width ≈ 10μm) were successfully mapped providing a composite topograph directly comparable with optical micrograph. The domain structure was confirmed using other techniques such as piezoresponse force microscopy and atomic force microscopy/scanning electron microscopy and optical observations on the etched crystal. Results show that combined use of multiple techniques is necessary to gain a consistent interpretation of the microstructure. Finally, domain evolution in BT under compressive mechanical loading was observed in-situ using optical and X-ray diffraction techniques providing a series of images that show ferroelastic transition. The domain configurations influence the switching behaviour and constitutive models that can account for such effects need to be developed. Quantitative and qualitative data presented in this thesis can assist model development and validation.

The highly parallel nature of the fundamental principles of quantum mechanics means that certain key resource-intensive tasks --- including searching, code decryption and medical, chemical and material simulations --- can be computed polynomially or even exponentially faster with a quantum computer. In spite of its remarkably fast development, the field of quantum computing is still young, and a large-scale prototype using any one of the candidate quantum bits (or 'qubits') under investigation has yet to be developed. Spin-based qubits in condensed matter systems are excellent candidates. Spins controlled using magnetic resonance have provided the first, most advanced, and highest fidelity experimental demonstrations of quantum algorithms to date. Despite having highly promising control characteristics, most physical ensembles investigated using magnetic resonance are unable to produce entanglement, a critical missing ingredient for a pure-state quantum computer. Quantum objects are said to be entangled if they cannot be described individually: they remain fundamentally linked regardless of their physical separation. Such highly non-classical states can be exploited for a host of quantum technologies including teleportation, metrology, and quantum computation. Here I describe how to experimentally create, control and characterise entangled quantum ensembles using magnetic resonance. I first explore the relationship between entanglement and quantum metrology and demonstrate a sensitivity enhancement over classical resources using molecular sensors controlled with liquid-state nuclear magnetic resonance. I then examine the computational potential of irreversible relaxation processes in combination with traditional reversible magnetic resonance control techniques. I show how irreversible processes can polarise both nuclear and electronic spins, which improves the quality of qubit initialisation. I discuss the process of quantum state tomography, where an arbitrary quantum state can be accurately measured and characterised, including components which go undetected using traditional magnetic resonance techniques. Lastly, I combine the above findings to initialise, create and characterise entanglement between an ensemble of electron and nuclear spin defects in silicon. I further this by generating pseudo-entanglement between an ensemble of nuclear spins mediated by a transient electron spin in a molecular system. These findings help pave the way towards a particular architecture for a scalable, spin-based quantum computer.

Ordered mesoporous materials have attracted much attention recently for use in a wide range of applications. The oxidising materials, ceria (CeO₂) and CGO (Ce₀.₉Gd₀.₁O[subscript(2-δ)]) have both been synthesised with ordered mesopores, but a method for the simple fabrication of these materials in high yields with crystalline pore walls has not yet been reported in the literature. This thesis details the development of the vacuum impregnation method for the synthesis of ordered mesoporous materials with emphasis on ceria and CGO. Using the vacuum impregnation method both materials were successfully prepared. The materials exhibited the porous single crystal morphology in high yields, with unusual crystallographic features. Nitrogen physisorption, transmission electron microscopy (TEM), TEM tomography and temperature programmed studies were employed. Temperature programmed studies showed the materials to be catalytically active at lower temperatures than traditionally-prepared ceria. Photovoltaic studies showed that the materials exhibited efficient exciton quenching. The observation of nanowire extrusion during the synthetic procedure assisted in the postulation of a mechanism for product formation in the vacuum impregnation method. The vacuum impregnation method was subsequently shown to be applicable to the synthesis of other materials, with encouraging results presented for ordered mesoporous carbon and Zr₀.₈₄Y₀.₁₆O[subscript(2-δ)]. The syntheses of ordered mesoporous La₀.₈₅Sr₀.₁₅GaO[subscript(3-δ)] and La₀.₇₆Sr₀.₁₉CoO[subscript(3-δ)] were unsuccessful.