<p>Understanding lithium-ion insertion/extraction mechanisms in battery electrode materials is of crucial importance in developing new materials with better cycling performance. In this thesis, these mechanisms are probed for two different potential cathode materials by a combination of electrochemical and single-crystal X-ray diffraction studies. The materials investigated are V₆O₁₃and cubic LiMn₂O₄spinel.</p><p>Single-crystal X-ray diffraction studies of lithiated phases in the Li_xV₆O₁₃ system (x=2/3 and 1) exhibit superlattice phenomena and an underlying Li⁺ ion insertion mechanism which involves the stepwise addition of Li⁺ions into a two-dimensional array of chemically equivalent sites. Each successive stage in the insertion process is accompanied by a rearrangement of the Li⁺ ions together with an electron redistribution associated with the reduction of specific V-atoms in the structure. This results in the formation of electrochemically active sheets in the structure. A similar mechanism occurs in the LiMn₂O₄ delithiation process, whereby lithium is extracted in a layered arrangement, with the Mn atoms forming charge-ordered Mn³⁺/Mn⁴⁺ layers.</p><p>Lithium-ion insertion/extraction processes in transition-metal oxides would thus seem to occur through an ordered two-dimensional arrangement of lithium ions extending throughout the structure. The lithium ions and the host structure rearrange cooperatively to form superlattices through lithium and transition-metal ion charge-ordering. A picture begins to emerge of a universal two-dimensional lithium-ion insertion/extraction mechanism analogous to the familiar staging sequence in graphite.</p>

Diamond is a promising material for high-power, high-frequency and high- temperature electronics applications, where its outstanding physical properties can be fully exploited. It exhibits an extremely high bandgap, very high carrier mobilities, high breakdown field strength, and the highest thermal conductivity of any wide bandgap material. It is therefore an outstanding candidate for the fastest switching, the highest power density, and the most efficient electronic devices obtainable, with applications in the RF power, automotive and aerospace industries. Lightweight diamond devices, capable of high temperature operation in harsh environments, could also be used in radiation detectors and particle physics applications where no other semiconductor devices would survive. The high defect and impurity concentration in natural diamond or high-pressure-high-temperature (HPHT) diamond substrates has made it difficult to obtain reliable results when studying the electronic properties of diamond. However, progress in the growth of high purity Single Crystal Chemical Vapor Deposited (SC-CVD) diamond has opened the perspective of applications under such extreme conditions based on this type of synthetic diamond. Despite the improvements, there are still many open questions. This work will focus on the electrical characterization of SC-CVD diamond by different measurement techniques such as internal photo-emission, I-V, C-V, Hall measurements and in particular, Time-of-Flight (ToF) carrier drift velocity measurements. With these mentioned techniques, some important properties of diamond such as drift mobilities, lateral carrier transit velocities, compensation ratio and Schottky barrier heights have been investigated. Low compensation ratios (ND/NA) &lt; 10-4 have been achieved in boron-doped diamond and a drift mobility of about 860 cm2/Vs for the hole transit near the surface in a lateral ToF configuration could be measured. The carrier drift velocity was studied for electrons and holes at the temperature interval of 80-460 K. The study is performed in the low-injection regime and includes low-field drift mobilities. The hole mobility was further investigated at low temperatures (10-80 K) and as expected a very high mobility was observed. In the case of electrons, a negative differential mobility was seen in the temperature interval of 100-150K. An explanation for this phenomenon is given by the intervally scattering and the relation between hot and cold conduction band valleys. This was observed in direct bandgap semiconductors with non-equivalent valleys such as GaAs but has not been seen in diamond before. Furthermore, first steps have been taken to utilize diamond for infrared (IR) radiation detection. To understand the fundamentals of the thermal response of diamond, Temperature Coefficient of Resistance (TCR) measurements were performed on diamond Schottky diodes which are a candidate for high temperature sensors. As a result, very high TCR values in combination with a low noise constant (K1/f) was observed.

In this licentiate thesis the work done in the project KME410 will be presented. The overall objective of this project is to evaluate and develop tools for designing against fatigue in single-crystal nickel-base superalloys in gas turbines. Experiments have been done on single-crystal nickel-base superalloy specimens in order to investigate the mechanical behaviour of the material. The constitutive behaviour has been modelled and verified by simulations of the experiments. Furthermore, the  microstructural degradation during long-time ageing has been investigated with  respect to the component’s yield limit. The effect has been included in the  constitutive model by lowering the resulting yield limit. Finally, the fatigue crack  initiation of a component has been analysed and modelled by using a critical plane approach. This thesis is divided into three parts. In the first part the theoretical framework, based upon continuum mechanics, crystal plasticity and the critical plane approach, is derived. This framework is then used in the second part, which consists of three included papers. Finally, in the third part, details are presented of the used  numerical procedures.

Understanding lithium-ion insertion/extraction mechanisms in battery electrode materials is of crucial importance in developing new materials with better cycling performance. In this thesis, these mechanisms are probed for two different potential cathode materials by a combination of electrochemical and single-crystal X-ray diffraction studies. The materials investigated are V6O13 and cubic LiMn2O4 spinel. Single-crystal X-ray diffraction studies of lithiated phases in the LixV6O13 system (x=2/3 and 1) exhibit superlattice phenomena and an underlying Li+ ion insertion mechanism which involves the stepwise addition of Li+ ions into a two-dimensional array of chemically equivalent sites. Each successive stage in the insertion process is accompanied by a rearrangement of the Li+ ions together with an electron redistribution associated with the reduction of specific V-atoms in the structure. This results in the formation of electrochemically active sheets in the structure. A similar mechanism occurs in the LiMn2O4 delithiation process, whereby lithium is extracted in a layered arrangement, with the Mn atoms forming charge-ordered Mn3+/Mn4+ layers. Lithium-ion insertion/extraction processes in transition-metal oxides would thus seem to occur through an ordered two-dimensional arrangement of lithium ions extending throughout the structure. The lithium ions and the host structure rearrange cooperatively to form superlattices through lithium and transition-metal ion charge-ordering. A picture begins to emerge of a universal two-dimensional lithium-ion insertion/extraction mechanism analogous to the familiar staging sequence in graphite.

Single crystals of sodium salt of guanosine dihydrate and 9 Ethyl Guanine were X-irradiated with the objective of identifying the radical products. Study with K-band EPR, ENDOR, and ENDOR-Induced EPR techniques indicated at least four radical species to appear in both crystals in the temperature range of 6K to room temperature. Three of these radicals (Radicals R1, R2, and R3) were present immediately after irradiation at 6K. Computational chemistry and EPR spectrum simulation methods were also used to assist in radical identifications. Radical R1, the product of net hydrogen addition to N7, and Radical R2, the product of electron loss from the parent molecule, were observed in both systems. Radical R3, in Na+.Guanosine-.2H2O, is the product of net hydrogen abstraction from C1' of ribose group and radical R3 in 9EtG was left unassigned due to insufficient experimental data. Radical R4, the C8-H addition radical, was also detected in both systems. For Na+.Guanosine-.2H2O, R4 was observed after warming the irradiated crystals to the room temperature. But for the 9EtG crystals the corresponding radical form was detected after irradiation at room temperature. Density functional theory (DFT) based computational studies was conducted to investigate the radical formation mechanisms and their stability. Here possibilities of proton transfers from the neighboring molecules were considered. The first approach was to consider the proton affinities of the acceptor sites and deprotonation enthalpies of the donor sites. This approach supported the formation of radicals observed in both systems. The second approach, applied only to the 9EtG system, was based on proton transfers between 9EtG base-pair anion and cation radicals. Even though the charge and spins were localized as expected, the computed thermodynamic data predicted that the proton transfer processes are unfavorable for both anionic and cationic base-pairs. This indicates the need for additional work to draw final conclusions. In addition, DFT methods were used to compute the geometries and hyperfine coupling constants of 9EtG derived radicals in both single molecule and cluster models. The calculated results agreed well with the experimental results.

When proteins and DNA interact, arginine and lysine are the two amino acids most often in close contact with the DNA. In order to understand the radiation damage to DNA in vivo, which is always associated with protein, it is important to learn the radiation chemistry of arginine and lysine independently, and when complexed to DNA. This work studied X-irradiated single crystals of L-lysine monohydrochloride dihydrate (L-lysine·HCl·2H2O) and L-arginine monohydrochloride monohydrate (L-arginine·HCl·H2O) with EPR, ENDOR, EIE techniques and DFT calculations. In both crystal types irradiated at 66K, the carboxyl anion radical and the decarboxylation radical were detected. DFT calculations supported these assignments. Specifically, the calculations performed on the cluster models for the carboxyl anion radicals reproduced the proton transfers to the carboxyl group from the neighboring molecules through the hydrogen bonds. Moreover, computations supported the identification of one radical type as the guanidyl radical anion with an electron trapped by the guanidyl group. In addition, the radical formed by dehydrogenation of C5 was identified in the L-arginine·HCl·H2O crystals irradiated at 66K. For both crystal types, the deamination radicals and the dehydrogenation radicals were identified following irradiation at 298K. Different conformations of main-chain deamination radicals were detected at 66K and at 298K. In L-lysine·HCl·2H2O, these conformations are the result of the different rotation angles of the side chain. In L-arginine·HCl·H2O, one conformation at 66K has no O-H dipolar protons while the others have two O-H dipolar protons. In L-lysine·HCl·2H2O, two radicals with very similar sets of hyperfine couplings were identified as the result of dehydrogenation from C3 and C5. Two other radicals in low concentration detected only at 66K, were tentatively assigned as the radical dehydrogenated from C3 and the side-chain deamination radical. In L-argnine·HCl·H2O, the radicals from dehydrogenation at C5 and C2 also were identified. DFT calculations supported these assignments and reproduced conformations of these radicals.Finally, based on the radicals detected in the crystal irradated at 66K and at 298K, the annealing experiments from the irradiation at 66K, and the previous studies on the irradiated amino acids, the mechanisms of the irradiation damage on lysinie and arginine were proposed.

In this paper the mechanical behaviour, both elastic and plastic, of single-crystal nickel-based superalloys has been investigated. A theoretic base has been established in crystal plasticity, with concern taken to the shearing rate on the slip systems. A model of the mechanical behaviour has been implemented, by using FORTRAN, as a user defined material model in three major FEM-programmes. To evaluate the model a simulated pole figure has been compared to an experimental one. These pole figures match each other very well. Yielding a realistic behaviour of the model.

The objective of this research is to use atomistic simulations to investigate dislocation nucleation from grain boundaries in face-centered cubic aluminum and copper. This research primarily focuses on asymmetric tilt grain boundaries and has three main components. First, this research uses molecular statics simulations of the structure and energy of these faceted, dissociated grain boundary structures to show that Σ3 asymmetric boundaries can be decomposed into the structural units of the Σ3 symmetric tilt grain boundaries, i.e., the coherent and incoherent twin boundaries. Moreover, the energy for all Σ3 asymmetric boundaries is predicted with only the energies of the Σ3 symmetric boundaries and the inclination angle. Understanding the structure of these boundaries provides insight into dislocation nucleation from these boundaries. Further work into the structure and energy of other low order Σ asymmetric boundaries and the spatial distribution of free volume within the grain boundaries also provides insight into dislocation nucleation mechanisms. Second, this research uses molecular dynamics deformation simulations with uniaxial tension applied perpendicular to these boundaries to show that the dislocation nucleation mechanisms in asymmetric boundaries are highly dependent on the faceted, dissociated structure. Grain boundary dislocation sources can act as perfect sources/sinks for dislocations or may violate this premise by increasing the dislocation content of the boundary during nucleation. Furthermore, simulations under uniaxial tension and uniaxial compression show that nucleation of the second partial dislocation in copper exhibits tension-compression asymmetry. Third, this research explores the development of models that incorporate the resolved stress components on the slip system of dislocation nucleation to predict the atomic stress required for dislocation nucleation from single crystals and grain boundaries. Single crystal simulations of homogeneous dislocation nucleation help define the role of lattice orientation on the nucleation stress for grain boundaries. The resolved stress normal to the slip plane on which the dislocation nucleates plays an integral role in the dislocation nucleation stress and related mechanisms. In summary, the synthesis of various aspects of this work has provided improved understanding of how the grain boundary character influences dislocation nucleation in bicrystals, with possible implications for nanocrystalline materials.

<p>In this paper the mechanical behaviour, both elastic and plastic, of single-crystal nickel-based superalloys has been investigated. A theoretic base has been established in crystal plasticity, with concern taken to the shearing rate on the slip systems. A model of the mechanical behaviour has been implemented, by using FORTRAN, as a user defined material model in three major FEM-programmes. To evaluate the model a simulated pole figure has been compared to an experimental one. These pole figures match each other very well. Yielding a realistic behaviour of the model.</p>

The primary goals of the research in this dissertation are to perform a systematic study to identify and understand the fundamental cause of prolonged processing time during transient liquid phase bonding of difficult-to-bond single crystal Ni-base materials, and use the acquired knowledge to develop an effective way to reduce the isothermal solidification time without sacrificing the single crystalline nature of the base materials. To achieve these objectives, a multi-scale numerical modeling approach, that involves the use of a 2-D fully implicit moving-mesh Finite Element method and a Cellular Automata method, was developed to theoretically investigate the cause of long isothermal solidification times and determine a viable way to minimize the problem. Subsequently, the predictions of the theoretical models are experimentally validated. Contrary to previous suggestions, numerical calculations and experimental verifications have shown that enhanced intergranular diffusivity has a negligible effect on solidification time in cast superalloys and that another important factor must be responsible. In addition, it was found that the concept of competition between solute diffusivity and solubility as predicted by standard analytical TLP bonding models and reported in the literature as a possible cause of long solidification times is not suitable to explain salient experimental observations. In contrast, however, this study shows that the problem of long solidification times, which anomalously increase with temperature is fundamentally caused by departure from diffusion controlled parabolic migration of the liquid-solid interface with holding time during bonding due to a significant reduction in the solute concentration gradient in the base material. Theoretical analyses showed it is possible to minimize the solidification time and prevent formation of stray-grains in joints between single crystal substrates by using a composite powder mixture of brazing alloy and base alloy as the interlayer material, which prior to the present work has been reported to be unsuitable. This was experimentally verified and the use of the composite powder mixture as interlayer material to reduce the solidification time and avoid stray-grain formation during TLP bonding of single crystal superalloys has been reported for the first time in this research.