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<p> Pure zinc and zinc/yttria stabilized zirconia (YSZ) composite coatings for combined wear and corrosion protection of ferrous substrates were prepared by electrodeposition using acidic zinc sulphate solutions containing YSZ and gelatin. The morphology of the electrodeposit was studied by Field Emission Scanning Electron Microscopy (FESEM) with energy dispersive spectroscopy (EDS). X-ray diffraction was employed to determine the texture of the zinc deposits. In the electrodeposition of pure zinc coatings, the influence of electrodeposition parameters, including current density, deposition time and solution pH was studied. It was found that the deposition rate was controlled by the current density and that an increase in deposition time resulted in the formation of deposit microstructures with coarse, columnar grains. The deposits prepared from solutions with lower pH were composed of uniform, fine grains and exhibited a basal plane preferred orientation.</p> <p> The effects of gelatin on zinc electrodeposition were investigated. It was found that the addition of gelatin profoundly modified the microstructure and crystallographic orientation of the zinc deposit. As the gelatin concentration increased, the mean grain size of zinc deposit was reduced and the basal plane preferred orientation was inhibited. The modification of the microstructure and orientation by gelatin increased microhardness of the zinc coating. However, the corrosion protection property which was assessed by potentiodynamic polarization test was not significantly changed.</p> <p> In the study on composite coatings, the incorporation of ceramic particles in the zinc deposit was characterized as a function of the deposition solution composition. The effect of ceramic particles on the hardness of the composite coatings was assessed by microhardness. The corrosion potential of the composite coating was determined by potentiodynamic polarization tests. The results showed that decrease in solution pH and addition of gelatin promoted the co-deposition of ceramic particles with zinc. The mechanical and corrosion properties of conventional zinc coatings were improved by the incorporation of ceramic particles.</p> / Thesis / Master of Applied Science (MASc)

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)

The objectives of this investigation are to develop a precise, non-destructive single crystal stress measurement technique, develop a model to explain the phenomenon known as 3power slump2, and investigate the role of device processing on wafer breakage. All three objectives were successfully met. The single crystal stress technique uses a least squares analysis of X-ray diffraction data to calculate the full stress tensor. In this way, precise non-destructive stress measurements can be made with known error bars. Rocking curve analysis, stress gradient corrections, and a data reliability technique were implemented to ensure that the stress data are correct. A theory was developed to explain 3power slump2, which is a rapid decrease in the amplifying properties of microwave amplifier circuits during operation. The model explains that for the particular geometry and bias configuration of the devices studied in this research, power slump is linearly related to shear stress at values of less than 90 MPa. The microscopic explanation of power slump is that radiation enhanced dislocation glide increases the kink concentration, thereby increasing the generation center concentration in the active region of the device. These generation centers increase the total gate current, leading to a decrease in the amplifying properties of the device. Passivation layer processing has been shown to both reduce the fracture strength and increase the residual stress in GaAs wafers, making them more susceptible to wafer breakage. Bare wafers are found to have higher fracture strength than passivated wafers. Bare wafers are also found to contain less residual stress than SiON passivated wafers, which, in turn, are found to have less stress than SiN passivated wafers. Topographic imaging suggests that SiN passivated wafers have larger flaws than SiON passivated wafers, and that the distribution of flaw size among SiN passivated wafers is wider than the distribution of flaws in SiON passivated wafers. These flaws are believed to lead to breakage of the device during processing, resulting in low fabrication yield. Both the power slump model and the wafer breakage data show that these phenomena are dependent on residual stress developed in the substrate during device fabrication. Reduction of process-induced residual stress should therefore simultaneously decrease wafer breakage rates and reduce power slump during device fabrication and operation. / Ph. D.

Magnetic nanoparticles are of considerable interest owing to their potential applications in biotechnology and the magnetic recording industry. Iron oxides have received much attention owing to their oxidative stability and biocompatibility; however, other transition metals and their alloys are also under investigation. Cobalt has one of the largest magnetic susceptibilities of these materials, but it readily oxidizes upon exposure to air resulting in antiferromagnetic oxide. Hence, coating cobalt nanoparticles with an oxygen-impermeable sheath would confer numerous benefits. Cobalt nanoparticles were prepared by the thermolysis of dicobalt octacarbonyl in two block copolymer micellar systems, wherein the copolymers were precursors to graphite or silica. Subsequent heat treatment of the samples at 600-700oC was conducted to condense the polymer coating around the cobalt nanoparticles and form oxygen impervious graphite or silica sheaths. Magnetic and structural characterization of these novel materials afforded pertinent information about their physical properties. Magnetic susceptometry indicated that the graphite coated cobalt nanoparticles resisted oxidation for over one year. The silica coated cobalt nanoparticles had high saturated specific magnetic moments, but the coatings were brittle and grinding the particles resulted in oxidation over time. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and energy-filtered TEM (EFTEM) were employed to study particle size and structural differences of the cobalt nanoparticles before and after heat treatment. The mean particle size and size distribution increased for the graphite coated cobalt particles, due to particle sintering at 700oC. In the silica coated cobalt nanoparticle system, the mean particle size increased when the sample was heat-treated at 600oC leading to a bimodal distribution. This bimodal distribution was explained by a fraction of the particles sintering, while others remained discrete. When the silica system was heat treated at 700oC, the particle size and size distribution remained similar to those of the pre-heat-treated sample, indicating that no sintering had taken place. The rapid pyrolysis of the polymer at 700oC may serve to lock the cobalt nanoparticles into a silica matrix, thus preventing them from coming into contact with one another and sintering. Several diffraction techniques (selected area electron diffraction (SAD), nano-beam electron diffraction (NBD) and x-ray diffraction (XRD)) were used to probe the crystal structure of graphite and silica coated cobalt nanoparticles, which was determined to be predominantly face-centered cubic. Anisotropic magnetic nanoparticles (nanorods) have an increased magnetophoretic mobility over spherical magnetic nanoparticles with the same equatorial radius. This property makes them attractive candidates for in vivo biological applications. Anisotropic mixed ferrite nanoparticles were coated with a biocompatible hydrophilic block copolymer to render them dispersible in aqueous media. Polymer coated mixed ferrite particles exhibited magnetic properties similar to that of pure magnetite, as the total level of other transition metals in the nanoparticulate system was less than 5%. Electron energy loss spectroscopy (EELS) and (EFTEM) confirmed that the dominant elements in the mixed ferrite nanoparticles were iron and oxygen. Furthermore, HRTEM, SAD and XRD analyses indicated that the crystal structure for the mixed ferrite nanoparticles was inverse spinel. X-ray diffraction peaks at low angles for the coated mixed ferrite rods corresponded to poly(ethylene oxide) peaks, suggesting that the block copolymer employed as a dispersant was associated with the particles. / Ph. D.

Piezoelectric materials find applications in multitude of devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based systems which are becoming serious problem owing to the restrictions imposed by regulatory agencies across the globe. In the functional ceramics community, currently there is no problem more important than to find a replacement for lead-based piezoelectrics used for actuators. The electromechanical properties required for actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are, however, far inferior to those of lead-based systems. There are three lines of research for addressing this fundamental problem "C (i) search for new systems through a combination of theory-based prediction followed by experimental effort (doping, solid solutions having a morphotropic (M) or polymorphic (P) phase boundary (PB), (iii) stabilization of metastable phases or finding the high temperature triclinic systems, and (iii) improving the properties of known compositions through microstructure optimization, domain engineering and multilayering. All these approaches are challenging and require innovation to make a significant impact on the current state-of-the-art. In this thesis, the later line of research was focused which is promising for near future applications, as it builds upon the known material systems with high depoling temperatures that have demonstrated the potential to be practical. In the first chapter, a novel method for the synthesis of lead-free (1-x)(Na0.5Bi0.5)TiO₃ "C xBaTiO3 piezoelectric ceramics was investigated. Initially, multiple compositions around morphotrpic phase boundary (MPB) were synthesized to identify the optimum composition 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) for electromechanical effect. The new synthesis method starts with the synthesis of Na2Ti6O13 (NTO) whiskers which are then transformed into lead-free NBT-BT ceramics. Synthesis of NTO whiskers was performed using molten salt synthesis (MSS) method. Tape casting method was used to align the whiskers in base matrix powder and subjected to various processing temperatures to elucidate the microstructure and texture evolution. For this, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis were used as principal tools. The sintering process can be understood by dividing it into three stages, namely (i) transformation of monoclinic whiskers in to NBT-BT perovskite phase through topochemical reaction (<800°C), (ii) localized sintering confined on single whisker (800-1050°C), and (iii) liquid phase sintering as densification and grain growth occurs in the whole matrix (>1050°C). The concentric growth ledges observed on grain surfaces were found to be preferably confined on the corners of cubical grains indicating <111> growth direction. The Lotgering factor (f100) for the sintered matrix was found to decrease with increase in sintering temperature. The longitudinal piezoelectric constant (d33) of samples sintered for 20h at 1175°C, 1200°C and 1225°C was measured to be ~153 pC/N, ~216 pC/N and ~180 pC/N, respectively. Next, a novel method was developed for the synthesis of nanostructured lead-free ferroelectric NBT-BT whiskers with high aspect ratio using NTO as a host structure. High energy x-ray diffraction coupled with atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of lead-free NBT-BT whiskers as rhombohedral, i.e. a ferroelectricity enabling type. The HRTEM analysis revealed local monoclinic-type structural distortions indicating a modulated structure at the nanoscale in the MPB composition of lead-free NBT-BT whiskers. The structural rearrangement during the synthesis of lead-free NBT-BT whiskers was found to occur via translation of edge shared octahedra of NTO into a corner sharing coordination. The high temperature morphological changes depicting disintegration of isolated whiskers into individual grains due to higher grain boundary energy have been found to occur in a close analogy with Rayleigh-type instability. In lead-based ABO3 compounds, with B-site disorder, the origin of enhancement of piezoelectric properties near MPB has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. In this thesis, a microscopic model derived from comparative analyses of HR-TEM and neutron diffraction was developed that explains the origin of high piezoelectric response in lead "C free MPB compositions of NBT-BT. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase were attributed to localized displacements of atoms along the non-polar directions. These results provide new insight towards design of high performance lead "C free piezoelectric materials. Microstructure and domain structure play dominant role towards controlling the magnitude of piezoelectric coefficient and hysteretic losses in perovskites. Brick-wall like microstructure with large grain size and small domain size can provide significant enhancement in the magnitude of piezoelectric coefficient. A synthesis technique for lead-free piezoelectric NBT-BT system that can provide [001]pc/[012]Rh grain oriented ceramics with large grain size and an electrical poling technique that results in smaller domain size will have significant impact on the electromechanical response. In this research, a synthesis technique was developed and the processing variables that play deterministic role in achieving the large grain brick-wall like microstructure were explained. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with applied electric field. The piezoelectric response was found to increase monotonously with the incease in the degree of texturing and optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient as compared to its random form. In order to understand the mechanism of enhanced piezoelectric response in textured NBT-BT, in-situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly-oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nano regions and internal stresses induced by domain switching. In conjunction to focus on NBT-BT, new lead-free piezoelectric materials with enhanced piezoelectric response were synthesized. This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO₃-xA(Cu1/3Nb2/3)O3₃ (A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large d33 of ~330 pC/N and electromechanical planar coupling constant (kp)~ 46% at room temperature. The piezoelectric instability in these compositions was found to increase with x despite monotonous decrease in the long range polar ordering. High energy X-ray diffraction coupled with PDFs indicated increase in local polarization. Raman scattering analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. These localized polar distortions were found to persist much above the Curie temperature (Tc). Polarization "C electric field (P-E) hysteresis loop analysis indicated presence of the internal bias that was found to be correlated with the formation of polar defects. This defect structure was found to modulate the domain structure resulting in nano domains and broad domain walls with higher mobility as revealed through analysis from HR-TEM and piezoresponse force microscopy (PFM). The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The electron paramagnetic resonance (EPR) investigations revealed that substitution of Cu²⁺ takes place on octahedral sites that are distorted due to Jahn-Teller effect. The A-sites were distorted by substitution of Sr and Ca on Ba-site possessing different ionic radii and electronegativity. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. As an application, the solid solution with nominal composition of (1-x)BaTiO₃-xBa(Cu1/3Nb2/3)O₃ (BCN) (x = 0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO₃ "C 0.025 Ba(Cu1/3Nb2/3)O₃ (y = 0.05, 0.06, 0.075, 0.1). Room temperature XRD patterns showed decrease in tetragonality of BT after modifying with BCN (BT-BCN). Modifications with Sn lead to further decrement in tetragonality and the room temperature structure became cubic at 6.0 at% doping level. The decrement in tetragonality was accompanied by lowering of Tc.  BT-BCN doped with 6 and 7.5 at% Sn were found to exhibit diffuse phase transition accompanied by high dielectric constant "Ý 7000, low loss tangent "Ü 1% and grain size in the submicron regime ("Ü 1 "Ìm). These compositions were found to be promising for Y5V type multilayer ceramic capacitors (MLCCs). Lastly, the dielectric and ferroelectric responses of compositionally graded bilayer and trilayer composites consisting of BT and 0.975BaTiO₃-0.025Ba(Cu1/3Nb2/3)O₃ (BT-BCN) were investigated. Two types of graded bilayer samples were synthesized, one with same thickness of BT and BT-BCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BT-BCN layers of equal thickness. SEM and TEM images showed a sharp interface with needle-shape domains across the interface. The domain size on BT-side was found to be larger than that on BT-BCN-side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting of characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BT-BCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from P"CE field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area, Pr and EC decreased with increasing frequency due to delayed response, but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. / Ph. D.

Ligaments and tendons are rope-like structures in our body that possess time- and history-dependent material properties. Despite the many advances made in experimental and theoretical biomechanics, the material properties of these biological structures are still not fully characterized. This dissertation represents a step forward in the development of combined theoretical and experimental tools that capture the time- and history-dependent material properties of ligaments and tendons. The mechanical behavior of bundles of collagen fibers which form ligaments and tendons was investigated. Axial stress-stretch data and stress relaxation data at different axial stretches were collected by testing rat tail tendon fascicles. The experimental results demonstrated, for the first time, that the shape of the normalized axial stress relaxation curve depends on the axial stretch level thus suggesting that the fascicles are nonlinear viscoelastic. A constitutive model was then formulated within the nonlinear integral representation frame- work proposed by Pipkin and Rogers (1968). Unlike the well-known quasi-linear viscoelastic model, the proposed constitutive law was able to capture the observed nonlinearities in the stress relaxation response of rat tail tendon fascicles. By extending the constitutive model for collagen fiber bundles, a new nonlinear three- dimensional model for the stress relaxation of skeletal ligaments was formulated. The model accounts for the contribution of the collagen fibers and the group substance in which they are embedded. Published uniaxial experimental data on the stress relaxation of human medial collateral ligaments were used to determine the model parameters. The model predictions for simple shear in the fiber direction, simple shear transverse to the fiber direction, and equibiaxial extension were then examined and, for the case of simple shear in the fiber direction, such predictions were found to be in good agreement with published experimental data. The relationship between the mechanical response and structure of suspensory ligaments was examined by performing state-of-the-art small angle x-ray diffraction experiments in tandem with incremental stress relaxation tests. Specifically, small angle x-ray diffraction was used to measure changes in strain and orientation of collagen fibrils during the stress relaxation tests. Throughout the tests the collagen fibrils were found to gradually orient towards the loading direction. However, the collagen fibril strain did not change significantly suggesting that collagen fibers do not play a significant role in dissipating load during stress relaxation. / Ph. D.