This investigation is based on the topochemical modification of three set of phases: Sr₃Co₂O₅Cl₂, SrO(Sr(Ru_0.5M_0.5)O₃)n (M = Ti, Mn, Fe; n = 1, 2, &infin;), and SrO(SrVO₃)n (n = 1, 2, &infin;). The topochemical reduction of Sr₃Co₂O₅Cl₂ using sodium hydride as a solid state reducing agent results in the formation of a reduced phase containing cobalt centres with an average oxidation state of +2 and an overall composition of Sr₃Co₂O₄Cl₂. The resulting material adopts a structure containing double sheets of square-planar corner-sharing CoO2 units separated by rock salt SrCl layers. Variable-temperature diffraction measurements reveal that these sheets undergo a cooperative Jahn-Teller distortion at T ~ 200 K due to unevenly filled degenerate (d_xy, d_yz) orbitals. This material adopts a magnetic structure in which the moments within each sheet are ordered antiferromagnetically, but the sheets are aligned ferromagnetically. An investigation was carried on the reduction behaviour of Ru-doped Sr(Ru_xFe_1-x)O₃. It was found that the reduction was non-topochemical for values of x > 0.5. For values of 0 < x < 0.5, no single phase precursor material could be formed. For the material with x = 0.5, reduction with CaH₂ produced a new phase with composition Sr(Ru_0.5Fe_0.5)O₂. This material is the first reported instance of Ru²⁺ in an extended transition metal oxide. DFT calculations reveal that, while the iron centres adopt a high-spin configuration, the ruthenium centres are in an intermediate-spin S = 1 configuration. Resulting competing magnetic interactions lead to frustration and lack of ordering. In order to further study the reduction behaviour of extended transition metal oxides containing ruthenium, the reduction of Sr₂(Ru_0.5Fe_0.5)O₄ and Sr₃(Ru_0.5Fe_0.5)₂O₇ was performed using CaH₂ as a solid state reducing agent. In these cases, reduction leads to segregation of the materials into multiple phases adopting closely related structures that differ mainly in their oxygen content. In these materials, the ruthenium centres are preferentially reduced, such that starting from materials containing Ru⁵⁺ and Fe³⁺, materials containing Ru^(3-δ)+ and Fe³⁺ are produced. Similarly, the low-temperature oxidation using CuF₂ as a solid state fluoride source was performed on materials with composition Sr3(Ru0.5M0.5)2O7 (M = Ti, Mn, Fe). In the case of M = Mn and Ti, materials with composition Sr₃(Ru_0.5Fe_0.5)₂O₇F₂ are produced in which the ruthenium centres are oxidised to Ru⁶⁺. For the M = Fe material, oxidation results in partial exchange of O for F and a material with composition Sr₃(Ru_0.5Fe_0.5)₂O_5.5F_3.5 in which the ruthenium centres are oxidised from +5 to +5.5 while the iron centres remain in a +3 oxidation state. While fluorination of the M = Ti leads to increasing itinerant electronic behaviour, fluorination of the M = Mn and Fe materials induces a twisting of the MX₆ octahedra that enables magnetic order to emerge at low temperatures. Finally, reaction of the SrO(SrVO₃)n (n = 1, 2, &infin;) series of phases with CaH₂ results in the formation of phases with composition SrO(SrVO₂H)_n (n = 1, 2, &infin;), the first examples of stoichiometric oxyhydride materials. SrVO₂H is magnetically ordered at room temperature, while the n = 1 and n = 2 materials order at 170 K and 240 K respectively. The high magnetic ordering temperature arises from strong interactions between (d_xy, d_yz) orbitals in a manner analogous to the reduced iron-containing phases SrO(SrFeO₂)_n.

<p> The following document is a compilation of four manuscripts which were peer-reviewed and accepted for publication in the following scientific journals: <em>Propellants, Explosives, Pyrotechniques</em>, <em>Crystal Growth & Design</em>, <em>Zeitschrift für Anorganische und Allgemeine Chemie ZAAC</em>, and <em>Energetic Materials Frontiers</em>. This work, also, includes excerpts from the author’s review of energetic materials synthesized via reactions with nitroacetonitrile published by <em>RSC Advances</em>. The research presented is the result of a four-year graduate program in the School of Materials Engineering and as part of the Purdue Energetics Research Center (PERC). </p> <p>  </p> <p><em>1,2,4-Triazine Based Energetic Materials and Improved Nitro-Compound Synthesis</em> briefly addresses the history of energetic materials, key requirements, and ways to modify materials to meet those requirements before transitioning to the research synthesis and characterization. The discussion sections address the synthesis methods of the heterocyclic 1,2,4-triazine structure and alternative routes for the formation of nitro moieties. Also discussed are the methods for chemical characterization, thermal stability, mechanical sensitivity, and the theoretical calculations used to obtain energetic performances for comparison with traditional known explosive materials.</p> <p><br></p>

<p>Flash sintering was first demonstrated in 2010, where a ceramic green body was rapidly densified within seconds by applying an electric field during the heating process. The ultra-fast densification can occur as current abruptly flows through the material and self-heats by Joule heating. This process has potentials for large energy savings due to the reduction in furnace temperatures and shortened sintering time compared to conventional sintering. In addition, the ultra-high heating and cooling rates, along with the impact of electric field and current leads to the formation of unique non-equilibrium features in ceramics, which could greatly enhance their properties. Despite the potential of flash sintering, there are many challenges in moving this technique towards practical applications, such as the microstructure inhomogeneity and lack of understanding of the defects characteristics.</p> <p>In this dissertation, flash sintering was performed on ZnO to investigate the influence of various electrical conditions on the microstructure and defects. Detailed characterization was performed on flash sintered ZnO with and without a controlled current ramp, and contrasting types of current (DC and AC). These parameters show significant impact on the gradient microstructure and defects, and provide a way to tailor the desired characteristics for a wide range of applications. On the other hand, flash sintering of ZnO performed with a high electric field and low current density resulted in the growth of nanostructures. These nanostructures are unique compared to other growth techniques as they contain high density basal-plane stacking faults, and exhibit ultraviolet excitonic emission and red emission at room temperature. The nanostructure growth mechanism was investigated by varying the current density limit and revealed the formation of liquid phases which allowed growth by the vapor-liquid-solid mechanism. These findings present a new exciting route for flash sintering to produce highly defective nanostructures for device applications with new functionalities.</p>

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.

<p>Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.</p> <p>First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃(BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.</p> <p> Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂thin film system, which has an insulating CeO₂in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.</p> <p> Third, the transition metal element in Bi₃MoM_TO₉(M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved. </p> <p> The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.</p><br>

As the demand for energy increases, competition for a sustainable alternative to non-renewable energy resources has resulted in the growth of the photovoltaic industry. Although most photovoltaic technologies are based on crystalline silicon, thin film technologies have been developed with the expectation of generating a comparably high-performing product with lower processing costs. These materials have demonstrated sufficiently high optoelectronic performance to enable commercialization but concerns such as material scarcity limit terawatt level power production.<div><br></div><div>In the continuous pursuit of earth abundant solar absorber materials appropriate for thin film technologies, enargite Cu3AsS4 has been identified as a promising material due to its ideal direct band gap, stability, and high absorption. Recent efforts have demonstrated this class of copper chalcogenides exhibits band gap tunability and has solution processing capabilities for potentially scalable manufacturing. Furthermore, recent first-principles calculations of enargite Cu3AsS4 have hypothesized this material may have high carrier mobility and defect-tolerant optoelectronic properties, which further support investigation into this material. <br></div><div><br></div><div>In this dissertation, a novel reactive deposition processing route has been developed which has produced dense, single-phase enargite thin films. A champion device efficiency of 0.54% was achieved following a post deposition etching procedure on these films, which demonstrates the density and observable secondary phases were not limiting to initial nanoparticle-based device performances. Together with recent modeling efforts, the non-ideal band alignment with both the back contact and diode junction is concluded to be the primary limiting factor for high efficiency devices. <br></div><div><br></div><div>As this technology contains arsenic, concerns have been raised about its potential carcinogenicity and toxicity. Similar concerns were raised during the development of cadmium telluride technology, but these concerns have been mitigated through careful life cycle analyses and identifying strategies for responsible life cycle management. Therefore, a life cycle analysis and two risk assessments have been completed on Cu3AsS4 systems. Although emissions of arsenic and its contributions to life cycle impacts are expected to be low due to the small quantity required, hot spots have been identified to reduce waste and emissions. Reduction strategies for this material system are found to be applicable to other PV systems and include minimizing molybdenum sputter waste, reusing and recycling balance of system components, and investigating low-energy processing routes on thin substrates. This work serves to establish a basis on which the potential environmental implications of this thin film technology are understood. <br></div><div><br></div><div>This dissertation will serve as a guide toward the technical and environmental development of Cu3AsS4 thin films. Having a life cycle perspective during the systematic development of a technology will enable sustainable engineering. Furthermore, the processing and characterization methods detailed herein are expected to be generally applicable to other copper chalcogenide systems. <br></div>

<p>New acceptor moieties with extended conjugation have been developed  for further understanding of structure-property relationships in donor-acceptor type semiconducting polymers. These diketopyrrolopyrrole or isoindigo based conjugated polymers have been demonstrated as functional materials in organic field effect transistors, photoacoustic imaging and organic electrochemical transistors. With demonstrations of semiconducting molecular design, we hope to spark new research directions especially on deeper investigation of charge transport dependence on chemical structures, and new design strategies of acceptor moieties with extended conjugation could be applied for targeted applications.</p>

The development of a vasculature within a tissue-engineered construct is one of the largest hurdles to successful bone regeneration. This thesis investigates methods to increase vasculature of such transplanted constructs, based on in vivo transplant studies and in vitro analysis of cell behaviors. A syngeneic mouse model in immunocompetent mice was developed and analyzed for both osteogenesis and hematopoiesis. This study demonstrates that syngeneic bone marrow stromal cells (BMSCs) are not rejected by the host, provided the strain of mice is sufficiently inbred. Additionally, an effective protocol was developed for the isolation of endothelial cells (ECs) from the bone marrow of mice. Two different sets of materials for this study were analyzed, both collagen based, and the GelfoamTM scaffold was found to possess advantages over synthesized collagen or collagen/hydroxyapatite composites, although only for mouse and not human bone transplantation. In order to gain rapid and integrated vasculature formation within the transplant, attempts were made to increase both (de novo) vasculogenesis and angiogenesis (ingrowth) from the surrounding tissue. For the former, transplant studies were combined with in vitro osteogenic calcification studies. Direct co-culture of the BMSCs and ECs increased osteogenic calcification and was monitored by using both alizarin red S quantification and quantitative polymerase chain reaction. Angiogenesis (as assessed by cell migration) was studied by various motility and chemotaxis assays in vitro, as well as through use of a directed in vivo angiogenesis assay. Growth factors, particularly TGF-β1 and BMP-4, were found to increase cell movement in these systems. In conclusion, we show that although much work remains to be done in order to increase the vasculature in bone transplants, systematic combination of in vivo and in vitro assays can elucidate the nature behind this crucial process in this context.

Hydroxyapatite (HAP) coatings are used in orthopaedic surgery for bone regeneration. Current methods of phase quantification of HAP coatings suffer from drawbacks. A novel methodology of quantitative phase analysis of HAP coatings has been devised and validated. This method, based on whole pattern fitting with a fundamental parameters approach, incorporates amorphous calcium phosphate (ACP) and apatite phases into structural refinements. A comparison of the structural and chemical properties of plasma sprayed (PS) and novel electrodeposited (ED) HAP coatings has been conducted. ED coatings contained less ACP and more preferred orientation than the PS coatings, although the stoichiometry was similar. In vitro investigations of PS and ED coatings in simulated body fluid and foetal calf serum revealed that both are bioactive. A carbonated apatite layer produced on the ED coatings was -0.7μm thick with a stoichiometry and chemical constituents similar to that of natural bone apatite. PS coatings produced a nanocrystalline carbonated apatite layer (-4μm). For the first time it has been possible to model crystalline HAP and nanocrystalline apatite as independent phases and obtain accurate lattice parameters for each. A positive linear correlation has been made between microstrain and the solubility of HAP and carbonated apatites. Dissolution studies have shown that the behaviour of HAP and carbonated apatite is dominated by crystallite size at low undersaturation and by crystallite size and microstrain at high undersaturation for crystallites between -30OA- 1000A. Metastable equilibrium occurred for crystallites <_400A at low undersaturation. Carbonate content did not affect the solubility or dissolution behaviour. A novel technology for coating polymeric tape with HAP for potential use in anterior cruciate ligament reconstruction has been devised. Mechanical tests have demonstrated that no adverse properties are induced by the coating technology. Cell culture studies have shown that the HAP layer is capable of enhanced attachment, proliferation and differentiation of osteoblast cells compared to uncoated tape.

Porous metal phosphonate framework materials were synthesised by solvothermal reaction of bis(α-aminomethylenephosphonic acid) ligands with divalent and trivalent metal cations. The syntheses and characterisation by NMR and, where possible, single crystal X-ray diffraction of seven bisphosphonic acid ligands, including N,N′-piperazinebis(methylenephosphonic acid) (H₄L), its racemic and enantiopure (R) 2-methyl (H₄L′ and R-H₄L′) and 2,5-dimethyl (H₄L′′) derivatives, and N,N′-4,4′-bipiperidinebis(methylenephosphonic acid) (H₄LL) are reported. Syntheses of the known phase Y₂(LH₂)₃·5H₂O and the new phases, STA-13(Y) (St Andrews microporous material No. 13) and Y₂(R-L′H₂)₃·4H₂O, from reactions of Y(AcO)₃ with H₄L, H₄L′ and R-H₄L′ respectively are reported. The as-prepared and dehydrated structures of each phase have been determined from either laboratory or synchrotron powder X-ray diffraction data. Reaction of Y(AcO)₃ and H₄L′′ is shown to form a phase with a different structure. The features determining which structure crystallises are discussed. Syntheses of other rare-earth forms of STA-13 (Sc³⁺, Gd³⁺–Yb³⁺) and the porosity of each phase to N₂ are reported. STA-13(Y) is the most porous form with loadings of ∼3 mmol g⁻¹ and ∼4 mmol g⁻¹ for N₂ and CO₂ respectively. MIL-91(Fe) was synthesised for the first time from reactions of Fe³⁺ cations with H₄L. Its structure was confirmed by Rietveld refinement, but it was not porous. The first syntheses of [Fe₄L₁.₅(AcO)₁.₅(OH,H₂O)₃]·0.5NH₄5.5H₂O (L= L or L′) are reported, from reactions of H₄L or H₄L′ in the presence of an excess of Fe³⁺ cations. The phase is related to a previously reported Co phase. The synthesis of divalent metal bisphosphonate STA-12(Mg) (Mg₂(H₂O)₂L·5.6H₂O) was reported for the first time and its structure determined from single crystal X-ray diffraction. The dehydration behaviour of this material was compared with the known forms of STA-12. STA-12(Mg) is porous to both N₂ (∼5.5 mmol g⁻¹) and CO₂ (~ 8.5 mmol g⁻¹). Reaction of H₄LL with Co²⁺ and Ni²⁺ gave two materials isoreticular with STA-12, labelled STA-16(Co) and STA-16(Ni). The structures of both materials were solved from synchrotron powder X-ray diffraction data. On dehydration, STA-16(Co) undergoes a reversible structural transition to an unknown structure. By contrast, STA-16(Ni) retains the same symmetry in the dehydrated form and its structure was determined from synchrotron powder X-ray diffraction data. Both materials are porous to N₂, with an uptake of up to 22.2 mmol g⁻¹, and CO₂ with maximum loading of 21.7 mmol g⁻¹. NLDFT analysis of N₂ adsorption data confirm the crystallographically determined pore radii. Syntheses of other frameworks with divalent cations and initial reactions of H₄LL with trivalent cations are also reported.