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Magnetically frustrated materials hold promise of unique behavior allowing for the novel study of quantum phenomena. Such materials are poised to become an integral foundation for technological advancement in the post-Silicon Age. Crystalline materials are given special focus where the rigid lattice allows more detailed study of these quantized effects and frustration behavior. As opposed to polycrystalline powders, large single crystals can be preferentially aligned enabling the study of anisotropic behavior. Two cubic structure types have garnered significant interest due to their 3-D tetrahedral arrangement of symmetry-related metal centers with the potential for magnetic frustration: pyrochlores and perovskites. The supercritical hydrothermal crystal growth technique has been applied to a host of refractory oxides to enhance phase purity and minimize crystalline defects often introduced by conventional flux or melt-based based techniques. The supercritical growth in aqueous alkali at temperatures much lower than those of floating zone melts, while maintaining a sealed environment, avoids the possibility for reactant sublimation. In comparison to melt-based techniques, the modest thermal conditions also aid in minimizing atomic site displacements by insertion into different sites than those expected (“stuffing”). Through supercritical hydrothermal conditions, it was possible to obtain the entire series of lanthanide stannate pyrochlores. Stannous oxide, originally applied for in situ ceria reduction, was found beneficial for all lanthanide oxide reactants regardless of oxidation state allowing facile growth of faceted, mm-scale stannate octahedra in only days. This has allowed for the first single-crystal neutron scattering study of the quantum spin liquid candidate Ce2Sn2O7 with similar experiments to follow across the lanthanide series. The sealed, pressurized supercritical hydrothermal technique was also applied in the growth of stoichiometric orthoscandates and site-ordered cubic barium double perovskites. Both systems had structures occur in crystallographic settings previously only possible through thin-film epitaxial growth or application of high pressures and temperatures. Attempts to expand the palette of lanthanide-containing germanium perovskites yielded novel P212121 LnTM(GeO4)(OH) (TM = 3d transition metal) adelite-type structures possessing chiral [TMO4]∞ a-axis chains. These adelites demonstrated the first known inclusion of lanthanides and germanium in the adelite-descloizite supergroup. The synthetic possibilities of the refractory lanthanide oxides and often-overlooked germanium offer great synthetic possibilities poised to further expand the adelite family while also providing a few magnetically frustrated surprises themselves or through the high-symmetry cubic garnet and spinel products encountered during exploratory adelite synthesis under hydrothermal conditions.

AbstractIn this work, microsized zeolite NaY was synthesized using a hydrothermal method with sodium silicate as the silicone source without the organic template. The chemical composition of reaction gel was determined, preparation of the precursor and the reaction conditions for hydrothermal reaction were studied and optimized. The reason for the production of side product Na-P1 was proposed and discussed.As a promising desiccant for wide applications, the water adsorption behavior of NaY and commercial Y type zeolite was investigated. Proton solid-state NMR spectra were used to investigate the bonding in the framework for different hydration standards of zeolite samples. Neutron images were taken to explore the hydration and dehydration pattern and diffusion style of bulk zeolite samples. The dehydration of the commercial and synthesized NaY zeolites was also explored. Finally, the composites of NaY zeolite and other types of materials, glass and polyurethane were designed and investigated, and could potentially be used for reproducible water adsorption process and work as energy-conserving material.

Bismuth iron oxide (BFO) crystals have potential for applications ranging from next-generation, magnetoelectricity-based electronics to photocatalysts for the breakdown of toxic chemicals. Hydrothermal synthesis (HTS) has been shown to be an attractive solution growth method for producing well-defined, phase-pure BFO crystals. Until now, research in this field has focused on understanding the relationships between external experimental parameters in HTS and resultant crystalline phases of BFO, neglecting the role of the solution chemistry in crystal phase determination. Two spectator cations, Na+ and K+, commonly used in HTS of BFOs were investigated for their potential roles in determining the phase outcome of the final products in relation to a recently discovered, time-dependent transformation of an intermediate phase that was found to strongly influence the final phase outcome. Synthesis of BFOs was performed using wet chemistry techniques and reaction in a high-pressure, low-temperature environment. Characterization was performed using powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Phase-pure BiFeO3 was confirmed to form in the presence of K+ only when the intermediate underwent transformation while phase-pure Bi2Fe4O9 could be formed in the presence of Na+ regardless of the status of the intermediate. A new synthetic method was developed to elucidate whether the cations affected the transformation of the intermediate, and whether this potential transformation was the cause of the phase control. It was found that the intermediate was not crystallographically affected by the cations and the presence of the cations themselves only during heat treatment determined the final phase of the product. Finally, a thought experiment was conducted that suggests a stabilization role for spectator anions and a formation mechanism for Bi2Fe4O9. The effects of cations on crystal morphology were inconclusive. The methods developed for these investigations and subsequent results lay the groundwork for a better understanding of the role of other ions in the HTS of BFOs.

Zeolites are considered as one of the key heterogeneous catalysts in refinery operations and petrochemistry processes. Researchers have been actively exploring new designs or concepts to foster the applications of zeolites in other fields. To improve the accessibility of active sites and reduce the diffusion limitations within micropores, various hierarchically organized pore systems have been architected based on the conventional microporous zeolites. Advances in zeolite synthesis and hierarchical structure design could bring about opportunities for new catalytic applications as well as improvements of current technological processes. However, the multilevel pore architectures complicate the understanding of their catalytic behaviors. Therefore, this dissertation has addressed the attempts on understanding the structure—activity relationship in hierarchical zeolites for maximal catalytic advantages and future rational catalyst design. Self-pillared pentasil (SPP) zeolite was selected as a prototype of hierarchical zeolites, and its formation mechanism was studied at the beginning of this dissertation. Different strategies were then developed to tailor the SPP zeolite structure and mesoporosity. Catalytic behavior of SPP zeolites was explored through studies of model reactions (i.e., benzyl alcohol self-etherification and alkylation with mesitylene). Key structural attributes to selectivity and catalytic efficiency were determined through kinetic studies. A quantitative analysis towards the catalytic contributions and diffusion resistance could assist the practical applications of SPP zeolites and other similar hierarchical zeolites in the future.

Cuprous delafossite oxides are a family of copper-based complex oxides uniquely structured with alternating layers of linearly coordinated O-CuI-O and MIIIO6 edge-shared octahedra. This structure is responsible for several interesting properties, such as p-type conductivity through a delocalized Cu 3d- and O 2p- orbital valence band, susceptibility to both extrinsic acceptor doping and oxygen intercalation, and high optical transparency. However, reported applications of these oxides have been relatively limited, especially compared to perovskite-structured oxides. One reason for this is likely the difficulties faced controlling morphology, impurities, and doping in their syntheses. The work presented here starts with this synthetic challenge, first focusing on the synthetic chemistry in understanding the phase formation and crystallization of CuScO2, then from the observed properties of CuScO2, the potential application of delafossite oxide as oxygen electrocatalysts is proposed and investigated.The properties of CuScO2, a potential p-type transparent conducting oxide, lead to several synthetic challenges. Significant oxygen intercalation within copper layer means control of oxidation proves difficult by the conventional solid state syntheses. Through consideration of copper and scandium species hydrolysis, the first hydrothermally synthesized pure-phase CuScO2 is reported. Post-annealing treatments were used to investigate the influence of oxygen intercalation and were found to increase copper oxidation, leading to increased light absorption, and flat-band potential shifts.The observed oxygen intercalation in CuScO2 led to an original research proposal and subsequent demonstration of cuprous delafossite oxides as catalysts for the alkaline oxygen reduction reaction. The delafossite structure possesses several key elements that could potentially make it desirable for ORR catalytic applications: the presence of low-coordination Cu-sites, accessible by O2 molecules, and the ability to alter lattice space around Cu-sites by changing the size of the MIII cation. CuLaO2 was found to have the most prevalent complete reduction of oxygen out the oxides tested.Finally, preliminary studies on the use of CuLaO2+x as a potential low temperature solid oxide fuel cell cathode material for low temperature oxygen reduction are presented. The experimental setup and custom fabricated cell holder are detailed, followed by electrochemical impedance spectroscopy tests to compare the oxide to commercially available cathode materials. The CuLaO2+x phase shows potential at very low temperature (< 400 °C), and promising new directions are discussed.Cuprous delafossite oxides provide a unique framework for tuning chemical and catalytic properties. Focus on individual copper and scandium species hydrolysis led to the first reported phase-pure CuScO2 hydrothermal synthesis. The presented rationale can be applied to other delafossite oxides, allowing for improved morphology and doping control. The first demonstration of cuprous delafossite oxides as alkaline oxygen reduction catalysts and investigation of their low temperature catalytic properties show the potential for tunable copper sites in a variety electrocatalytic processes involving oxygen species.

One of the thrust areas of our research deals with exploratory synthesis of new inorganic-organic hybrid materials for energy storage. It is well-known that relevant to the research described later in this thesis, inorganic-organic hybrid solids studied thus far are largely made of coordination complexes where the organic molecules are acting like a ligand to coordinate around metal cations. In this research, we will employ polyoxometalate (POM) anions as an inorganic building block to replace otherwise oppositely charged metal cations in hopes to synthesize extended hybrid frameworks with rich redox chemistry. POM clusters are made of aggregates of transition-metal (TM) oxide units and can be employed as a charge reservoir during multi-electron chemical reactions involving multiple TM cations. These inorganic clusters possess an unmatched range of physical (such as magnetism) and chemical properties, acting as a set of transferable building blocks that can reliably be utilized in the formation of new materials with desired functionalities associated with versatile electronic structures.15,16 One of the challenges is of course to imagine how these anionic clusters could interact with organic molecules that are necessary for the formation of new hybrids. We anticipate, therefore, that the 'coordination' chemistry between POM anions and organic molecules is going to be different than that observed in the conventional hybrids based on metal cations. This thesis study will take an initial step to explore this new chemistry and to illustrate the structure and bonding of resulting solids for our continued research development in POM-based hybrids. The major focus of my study is about the synthesis and characterization of new extended solids made of, more specifically, polyoxovanadate (POV) and 4,4'-bipyridine (bpy) organic molecules through self-assembly

This dissertation is a two-part manuscript highlighting the utilities of the hydrothermal method for exploring phase space, then extending that to the targeted growth of potentially useful materials. Chapters 3 - 5 discuss the synthesis of Group 4 fluorides and oxyfluorides. The study of this class of compounds in regards to their single crystal structures is a rich, but neglected area. Among the Group 4 metals, compounds based on Zr and Ti have been extensively studied, while those based on Th and Hf are sparsely reported and those based on Ce(IV) are nearly completely neglected. Using the hydrothermal method, many new thorium, cerium(IV), and hafnium fluorides containing monovalent ions were synthesized and characterized. These systems exhibit great sensitivity toward both size and concentration of the monovalent metal in addition to experimental conditions such as temperature and reaction time. Interestingly, the descriptive and structural chemistries in the hafnium fluoride systems differ greatly from the thorium fluoride systems while showing no less structural variety. However, the structural chemistry in the cerium fluoride system acts as a bridge between thorium and hafnium fluoride systems. Crystal structures in these systems are introduced and discussed to describe the rich and varied chemistry. Several compounds exhibit luminescence from X-ray and UV-Vis excitations, and this interesting optical behavior is also discussed. Chapters 6 and 7 focus on using the hydrothermal method to grow crystals having other sorts of optical functionality. A particularly rich system in this sense is the rare earth (RE) borate system, which can be useful for nonlinear optical (NLO), lasing, and scintillator applications. In particular, YBO3 appears to be an especially versatile host, as it has an acentric crystal structure and can accommodate a wide range of rare earth dopants such as Nd(III), Er(III), and Yb(III), which can be used to generate lasing activity. Surprisingly, few single crystals of RE-doped YBO3 have been synthesized; in fact, recent work on RE-doped YBO3 powders has focused primarily on Eu(III). The absorption and emission spectra of the dopants in YBO3 show a definitive blue-shift of up to 10 nm as compared to the commonly-used laser hosts of yttrium aluminum garnet (YAG) and YVO4, and initial findings show comparable emissions to that of RE-doped YAG and YVO4. Another group of acentric borates, Na3(RE)9O3(BO3)8 (RE = Pr, Nd, Sm), were discovered in the process of synthesizing the RE-doped YBO3 compounds. Absorption/emission spectroscopy and lifetime measurements of these borates will also be discussed.

Sodium titanate nanoribbons and nanotubes were synthesised by hydrothermally ageing Aeroxide P25 in 10M NaOH at temperatures between 150 and 200°C. The Na1.48H0.52Ti3O7 nanoribbons comprised a layered TiO6 nanosheet framework with sodium and hydrogen cations interspersed between the sheets. Nanoribbon/nanosheet formation occurred via an amorphous (Ti-O-Na) intermediate phase. At milder temperatures (i.e. 150°C), the kinetics of nanosheet formation are slow enough to allow for their rolling up leading to nanotube formation. Acid washing converted the structure into hydrogen titanate (H2Ti3O7) by ion-exchange and provided uniform nanoribbons and nanotubes. Heat treatment of hydrogen titanate transformed nanotubes to anatase, while nanoribbon transformation to anatase occurred via a TiO2(B) intermediate phase. The enhanced stability provided by the nanoribbon architecture preserved a dominant {010} crystal facet at temperatures higher than 700°C. Nanotube thermal stability was improved by nitric acid treatment. Methanol and oxalic acid photodegradation performance was the highest at calcination temperatures of 500°C for nanotubes and 800°C for nanoribbons. The nanotube optimum represented a transition between the dominance of surface area and crystal phase, while nanoribbon performance was governed primarily by crystal phase. Despite both nanostructures producing particles with similar physical characteristics when calcined at 800°C the particles originating from the nanoribbons exhibited superior photoactivity. This difference was attributed to a greater percentage of {010} crystal facet in these particles which is beneficial for hydroxyl radical generation. The photocatalytic activity of Na1.48H0.52Ti3O7, Na2Ti6O13, H2Ti3O7 nanoribbons and anatase TiO2 nanorods were compared for water splitting, oxalic acid photodegradation and H2/O2 generation using sacrificial agents. The intrinsic properties of the materials affected their performance depending on the particular reaction. The Na2Ti6O13, in the presence of RuO2 co-catalyst, outperformed the TiO2, for the water splitting reaction, generating over 10 times more H2/O2. This derived from their tunnel-like structure which provided better electron/hole separation when compared with TiO2. However, the efficient holes and electrons scavenging in the presence of sacrificial agents overwhelmed the tunnel-like structure effect. In this case photoactivity was governed by the crystal structure: TiO2>Na2Ti6O13>H2Ti3O7~Na1.48H0.52Ti3O7 and by the band gap of the semiconductor which determined its capacity to absorb photons in producing electron/hole pairs.

Cerium oxide (ceria, CeO2-x where x is 0 to 0.5) has been one of the most widely used heterogeneous catalysts particularly in three way catalytic converters. Most of the catalytic traits can be attributed to two properties of ceria: first, the high mobility and storage capacity of oxygen within the lattice; second, the ease with which cerium changes between Ce3+ and Ce4+ states. These properties, combined with the abundance of cerium on earth, make ceria a low-cost highly effective alternative to noble metal catalysts. Recent research has been focused on the nanoscale properties of ceria. The effect on the catalytic activity of cerium oxide caused by varying the density of oxygen vacancy defects (OVD) has not been previously studied experimentally. This is due to the perceived inability to engineer stable defects not attributed to the presence of dopant atoms. It was found that the number of stable OVDs on cerium oxide nanoparticles and nanotubes can be increased with annealing at elevated temperatures under low pressure. The oxidative catalytic activity of these nanostructured catalysts was evaluated. Samples with higher densities of OVD were found to have much lower light-off temperatures when compared to that of their bulk counterpart. The chemical equilibrium reactions on the catalysts surface under low pressure were hypothesized to explain the unusual increase in the OVD density of the reported cerium oxide nanostructured catalysts. Cerium oxide is well known to exfoliate from the surface of cerium metal in the same way that rust exfoliates from iron or steel. A two-step process to fabricate nanoporous ceria membranes via anodization and subsequent calcinations is reported. These membranes have the potential to be used in solid oxide fuel cells and solid-state oxygen sensors. Cerium metal foil was first anodized into adherent porous cerium hydroxide film, followed by calcination for conversion into ceria membranes. These membranes are composed of ribbon-like structures that form the backbone of the porous framework. A proposed anodization model for the growth of the nanoribbons is discussed. Adviser Chin Li Cheung

A new “bottom-up” paradigm of electronics offers the possibility of assemblingvirtually any electronic device using nanoscale building blocks to provide functionality.Essential to this vision is the synthesis of such building blocks with customized composition, morphology, and properties in a reproducible, controlled manner.In the case of functional oxides, extensive studies have been carried out synthesizingall-oxide nanowires that are assembled across metal contact-pad electrodes to createdevices. However, there are drawbacks to this approach including: high ohmic losses;the active oxide region is determined by spacing of the electrodes; the contacts made tothe functional segment are on the side-wall of the nanowire; and making reproduciblecontacts over a range of devices is difficult.In this context, metal-oxide-metal (MOM) heterojunction nanowires, where twoAu nanowires are separated by a nanoscale segment of a functional oxide, offer severaladvantages over all-oxide nanowires. The MOM nanowire structure precisely defines theactive oxide region within the building block itself and the metal interconnects are integrated within the building block making them more suitable for device assembly. In addition, the small interfacial area of the metal interconnects to the oxide offer the possibility of measuring coupled electronic properties of nanoscale volumes of oxides without substrate effects.In this work, a novel method is developed to synthesize Au-TiO2-Au, Au-BaTiO3-Au and Au-PbTiO3-Au MOM heterojunction nanowires. This is the first report of successful synthesis of MOM nanowires with ternary oxides. Results from the synthesis and characterization of these nanowires are presented.In order to measure properties of these nanowires, single-nanowire-based devicesare fabricated using the focused ion beam (FIB) direct write method to make connectionsto macroscale electrode pads. The charge transport properties are measured and show anon-linear, non-rectifying response. This response is shown to be due to a transition between ohmic and space-charge-limited-conduction (SCLC) and is investigated using Au-NiO-Au nanowires as a model system. In the Au-BaTiO3-Au and Au-PbTiO3-Au nanowire system, ferroelectric polarization measurements are performed using both electrical measurements and a scanning probe microscope approach.

Hybrid inorganic-organic networks have been studied in both chemistry and materials science due to properties, (e.g. porosity, magnetic and electronic behaviors) that may lead to applications in catalysis, gas absorption and storage. It is important to understand the different structural topologies shown by hybrid networks to help develop practical applications for these materials. The research is focused on the design and synthesis of well-defined hybrid network structures that have potential to contain molecular size cavities that can be used for catalysis and gas storage. In the field of organic-inorganic hybrid networks, the goals are to design and synthesize 1D, 2D and 3D networks with cavities, and to characterize them by X-ray, TGA and surface area measurements. Twenty-six networks have been successfully made with interesting structure topologies. These hybrid network structures are classified into three series based on their ligands. Series I contains ten hybrid networks constructed from the flexible ligand, 4, 4′-trimethylenedipyridine (TMDP), Zn2+ ions, and H3PO3, and with aromatic alcohols as templates to direct the formation of various hybrid network structures. Series II consists of five structures constructed from the relatively rigid ligand, 4, ′-bisimidazolelybipyridine (BIB) with metal ions (Cu2+, Ni2+) and the conjugated bases of H3PO3 and H3PO4. The BIB ligand is not commercially available so is produced and characterized by NMR, mass spectrometry and TGA. Rigid network structures were expected to construct with pores of molecular dimensions with the BIB ligand. To date, the BIB ligand has not yield the desired porous network, however, these 3D hybrid networks have interesting topologies, one of which is an interdigitated network that is the precursor for 3D interpenetrated networks. Series III contains five hybrid structures constructed from various organic ligands, such as tartaric acid, picolinic acid and 1, 2, 4-triazole. In addition to the hybrid networks, six hydrogen bonded networks were prepared. Graph-Analysis is applied to study these hydrogen bonded network structures. The Ï â ¦.Ï interaction is also discussed within the hydrogen bonded networks.

Cadmium Selenide (CdSe), a type of semiconductor nanocrystal, is of interest because its optical properties can be tuned by varying its size, thus yielding a material that has potential application in electronics and biology. Conventional preparations of CdSe primarily use organic solvents. We explored the use of high-temperature liquid water (HTW) as an alternative reaction medium because of its environmental benignity and solvent properties which could potentially mimic the function of the conventional organic-based mediums. The base case experimental conditions for the feasibility study (non-isothermal conditions) produced nanocrystals that exhibited quantum confinement behavior. The quantum yield (QY) for the base case nanocrystals was 1.5%, but was easily increased to ~7% by adding a cadmium sulfide (CdS) shell. The nanocrystal mean size increased with increasing reaction time, temperature, stabilizer concentration and Cd:Se molar ratio. The mean size decreased with increasing pH. Under isothermal synthesis conditions, nanocrystals smaller than those produced in the feasibility study were obtained when using the same process parameters.. The mean nanocrystal size did not increase with reaction temperature, but did increase with time and stabilizer concentration. The mean size also decreased with increasing pH and Cd:Se molar ratio. An increase in the Cd:Se molar ratio, pH and Cd:stabilizer molar ratio increased the QY. The reaction temperature and time had no affect on QY. We used red-shift rates and reaction completion times to determine an activation energy Q for the CdSe growth in HTW. We calculated Q = 0.48 ± 0.06 eV/molecule from the red-shift rate method and Q = 0.42 ± 0.08 eV/molecule using reaction completion times. Compared with organic-based systems, these values are lower, possibly due to the less bulky cadmium complex used. The kinetics analysis shows that the synthesis in HTW could be both reaction- and diffusion-controlled. This work indicates that HTW is a viable alternative reaction medium. Nanocrystals can be grown that exhibit quantum confinement, and certain process parameters have a profound effect on the nanocrystal’s quality. Further studies can identify the optimum process conditions to produce the nanocrystal with the highest quality.