ZnO and ZnO-TiO2 ceramics have intriguing electronic and mechanical properties and find applications in many fields. Many of these properties and applications rely on the understanding of defects and defect processes in these oxides as these defects control the electronic, catalytic and mechanical behaviors. The goal of this dissertation is to systematically study the defects and defects behaviors in Wurtzite ZnO and Ilmenite ZnTiO3 by using first principles calculations and classical simulations employing empirical potentials. Firstly, the behavior of intrinsic and extrinsic point defects in ZnO and ZnTiO3 ceramics were investigated. Secondly, the effect of different surface absorbents and surface defects on the workfunction of ZnO were studied using DFT calculations. The results show that increasing the surface coverage of hydrocarbons decreased the workfunction. Lastly, the stacking fault behaviors on ilmenite ZnTiO3 were investigated by calculating the Generalized Stacking Fault (GSF) energies using density functional theory based first principles calculations and classical calculations employing effective partial charge inter-atomic potentials. The gamma-surfaces of two low energy surfaces, (110) and (104), of ZnTiO3 were fully mapped and, together with other analysis such as ideal shear stress calculations.

β-Ti alloys are widely used in airframe and biomedical applications due to their high ductility, high hardenability, and low elastic modulus. The phase transformations in β-Ti alloys are rather complex due to formation of metastable phases during various thermo-mechanical treatments. One such critical metastable phase, the hexagonal omega (ω) phase, can form in β-Ti alloys under quenching from the high temperature β phase and/or isothermal aging at intermediate temperature. Despite a substantial amount of reported works on the ω phase, there are several critical issues related to the ω formation need to be resolved, e.g. role of alloying elements and oxygen content. Therefore, this dissertation has attempted to provide insights into ω transformation in low misfit (Ti-Mo) and high misfit (Ti-V) binary systems as well as multicomponent (Ti-Nb-Zr-Ta) alloys. The evolution of ω structure, morphology and composition from the early stage (β-solution+quenched) to later stages after prolonged aging are systematically investigated by coupling transmission electron microscopy (TEM), atom probe tomography (APT) and high-energy synchrotron X-ray diffraction techniques. The influence of aging temperature and duration on characteristic of ω phase in Ti-Mo, and Ti-V alloys is addressed in details. It is found that compositional changes during aging can alter the structure, …

The widespread use of electronics in more avenues of consumer use is increasing. Applications range from medical instrumentation that directly can affect someone's life, down hole sensors for oil and gas, aerospace, aeronautics, and automotive electronics. The increased power density and harsh environment makes the reliability of the packaging a vital part of the reliability of the device. The increased importance of analog devices in these applications, their high voltage and high temperature resilience is resulting in challenges that have not been dealt with before. In particular packaging where insulative properties are vital use polymer resins modified by ceramic fillers. The distinct dielectric properties of the resin and the filler result in charge storage and release of the polarization currents in the composite that have had unpredictable consequences on reliability. The objective of this effort is therefore to investigate a technique that can be used to measure the polarization in filled polymer resins and evaluate reliable molding compounds. A valuable approach to measure polarization in polymers where charge release is tied to the glass transition in the polymer is referred to as thermally stimulated depolarization current (TSDC) technique. In this dissertation a new TSDC measurement system was designed and fabricated. …

The recent advancements in electronics and the advents of small scaled instruments has increased the attachment of life and functionality of devices to electrical power sources but at the same time granted the engineers and companies the ability to use smaller sources of power and batteries. Therefore, many scientists have tried to come up with new solutions for a power alternatives. Piezoelectric is a promising material which can readily produce continuous electric power from mechanical inputs. However, their power output is dependent upon several factors such as, system natural frequency, their position in the system, the direction of vibration and many other internal and external factors. In this research the working bandwidth of the system is increased through utilizing of two different piezoelectric beam in different directions. The dependency of output power with respect to rotation angle and also the frequency shift due to the rotation angle is studied.

Lack of crystalline order and microstructural features such as grain/grain-boundary in metallic glasses results in a suite of remarkable attributes including very high strength, close to theoretical elasticity, high corrosion and wear resistance, and soft magnetic properties. In particular, low coercivity and high permeability of iron and cobalt based metallic glass compositions could potentially lead to extensive commercial use as magnetic heads, transformer cores, circuits and magnetic shields. In the current study, few metallic glass compositions were synthesized by systematically varying the iron and cobalt content. Thermal analysis was done and included the measurement of glass transition temperature, crystallization temperature, and the enthalpies of relaxation and crystallization. Magnetic properties of the alloys were determined including saturation magnetization, coercivity, and Curie temperature. The coercivity was found to decrease and the saturation magnetization was found to increase with the increase in iron content. The trend in thermal stability, thermodynamic properties, and magnetic properties was explained by atomic interactions between the ferromagnetic metals and the metalloids atoms in the amorphous alloys. Mechanical behavior of iron based metallic glasses was evaluated in bulk form as well as in the form of coatings. Iron based amorphous powder was subjected to high power mechanical milling and …

In this study, four different NiTi-based shape memory alloys (SMAs) compositions were processed, shape-set, and characterized to evaluate their effectiveness as SMA actuation component for satellite antennas. Three of the compositions were commercially available NiTi wires (90°C Flexinol® actuator NiTi wire and Confluent ADB SE508 NiTi wire), NiTi SM495 plates (ATI Specialty Alloys and Components) and the other composition was in house lab-produced NiTiCu plate. Different shape-setting techniques were performed such as pin and plate, fixtures and dies, and finally a sandwich fixture. The two most promising outcomes were the SE NiTi 508 wire and the NiTiCu plate. A SE NiTi 508 wire was first heat-treated at 550 °C for 3 hours and then it was shape-set at 450 °C for 30 min using a Cu tube which was previously deformed to the desired deployment curvature and fixed on a steel rig. The wire was kept inside the Cu tube during the shape-setting process to obtain the desired curvature. After shape-setting, the wire was thermally cycled multiple times. The results showed that the SE NiTi 508 wire was able to retain its deployment shape successfully after each thermal cycle. Furthermore, a NiTiCu plate was sandwiched between two steel sheets which …

In this dissertation, tribo-corrosion behavior of several single-phase and multi-phase high entropy alloys were investigated. Tribo-corrosion of body centered cubic MoNbTaTiZr high entropy alloy in simulated physiological environment showed very low friction coefficient (~ 0.04), low wear rate (~ 10-8 mm3/Nm), body-temperature assisted passivation, and excellent biocompatibility with respect to stem cells and bone forming osteoblast cells. Tribo-corrosion resistance was evaluated for additively manufactured face centered cubic CoCrFeMnNi high entropy alloy in simulated marine environment. The additively manufactured alloy was found to be significantly better than its as-cast counterpart which was attributed to the refined microstructure and homogeneous elemental distribution. Additively manufactured CoCrFeMnNi showed lower wear rate, regenerative passivation, less wear volume loss, and nobler corrosion potential during tribo-corrosion test compared to its as-cast equivalent. Furthermore, in the elevated temperature (100 °C) tribo-corrosion environment, AlCoCrFeNi2.1 eutectic high entropy alloy showed excellent microstructural stability and pitting resistance with an order of magnitude lower wear volume loss compared to duplex stainless steel. The knowledge gained from tribo-corrosion response and stress-corrosion susceptibility of high entropy alloys was used in the development of bio-electrochemical sensors to sense implant degradation. The results obtained herewith support the promise of high entropy alloys in outperforming currently used …

This dissertation tested the hypothesis that energy transferred from a plasma or plume can be used to optimize the structure, chemistry, topography, optical and electrical properties of pulsed laser deposited and sputtered thin-films of ZnO, a-BOxNy, and few layer 2H-WS2 for transparent electronics devices fabricated without substrate heating or with low substrate heating. Thus, the approach would be compatible with low-temperature, flexible/bendable substrates. Proof of this concept was demonstrated by first optimizing the processing-structure-properties correlations then showing switching from accumulation to inversion in ITO/a-BOxNy/ZnO and ITO/a-BOxNy/2H-WS2 transparent MIS capacitors fabricated using the stated processes. The growth processes involved the optimization of the individual materials followed by growing the multilayer stacks to form MIS structures. ZnO was selected because of its wide bandgap that is transparent over the visible range, WS2 was selected because in few-layer form it is transparent, and a-BOxNy was used as the gate insulator because of its reported atomic smoothness and low dangling bond concentration. The measured semiconductor-insulator interfacial trap properties fall in the range reported in the literature for SiO2/Si MOS structures. X-ray photoelectron spectroscopy (XPS), Hall, photoluminescence, UV-Vis absorption, and X-ray diffraction (XRD) measurements investigated the low-temperature synthesis of ZnO. All films are nanocrystalline with …