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Yes / Emtricitabine (ECB) afforded dimorphic cocrystals (Forms I, II) of benzoic acid (BA), whereas with p-hydroxybenzoic acid (PHBA), p-aminobenzoic acid (PABA) are resulted in as high Z'' cocrystals. Intriguingly, the Z'' of cocrystals are trends from two to fourteen based on the manipulation of functional groups on the para position of BA (where H atom is replaced with that of OH or NH2 group). ECB‒PABA cocrystal consists of six molecules each and two water molecules in the asymmetric unit (Z''=14) with 2D planar sheets represents the rare pharmaceutical cocrystal. The findings suggest that the increment of H bond donor(s) systematically via a suitable coformer are in correspondence with attaining high Z'' cocrystals. Further, solid state NMR spectroscopy in conjunction with single crystal X-ray diffraction are demonstrated as significant tools to enhance the understanding of the number of symmetry independent molecules in the crystalline lattice and provide insights to the mechanistic pathways of crystallization. / Department of Science and Technology (DST) Fund for improvement of S & T Infrastructure (FIST) with grant no. SR/FST/CST-266/2015(c) to PS and VP. AN and VV acknowledge the Government of India under National Overseas Scholarship (2012-13) and High Commission of India, London UK for PhD studentship.

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Three-dimensional porous single crystals (PSCs) are a recent development in the growing world of mesoporous material. The mesoporosity allows for the material to retain their nanoproperties whilst being bulk in size. The current work concentrates on chromium oxide and cobalt oxide PSCs formed in the templates SBA-15 and KIT-6. HRTEM is the main technique used in this investigation, looking at the morphology and single crystallinity of these materials. A growth mechanism for the PSC material is proposed based on HRTEM observations. XRD studies revealed that the confinement effect, caused by the mesopores, reduces the temperature for both cobalt and chromium oxide crystallisation, as well as a different intermediate route from the metal nitrates. The properties of chromium oxide PSC are also investigated magnetically and catalytically. Some metal oxides in different templates are also presented, despite no PSC forming. HRTEM work on other nanomaterials, based on collaboration, is also presented.

Scanning Laser Epitaxy (SLE) is a new layer-by-layer additive manufacturing process being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. SLE allows for the fabrication of three-dimensional objects with specified microstructure through the controlled melting and re-solidification of a metal powder placed atop a base substrate. This dissertation discusses the work done to date on assessing the feasibility of using SLE to both repair single crystal (SX) turbine airfoils and manufacture functionally graded turbine components. Current processes such as selective laser melting (SLM) are not able to create structures with defined microstructure and often have issues with warping of underlying layers due to the high temperature gradients present when scanning a high power laser beam. Additionally, other methods of repair and buildup have typically been plagued by crack formation, equiaxed grains, stray grains, and grain multiplication that can occur when dendrite arms are separated from their main dendrites due to remelting. In this work, it is shown that the SLE process is capable of creating fully dense, crack-free equiaxed, directionally-solidified, and SX structures. The SLE process, though, is found to be currently constrained by the cumbersome method of choosing proper parameters and a relative lack of repeatability. Therefore, it is hypothesized that a real-time feedback control scheme based upon a robust offline model will be necessary both to create specified defect-free microstructures and to improve the repeatability of the process enough to allow for multi-layer growth. The proposed control schemes are based upon temperature data feedback provided at high frame rate by a thermal imaging camera. This data is used in both PID and model reference adaptive control (MRAC) schemes and drives the melt pool temperature during processing towards a reference melt pool temperature that has been found to give a desired microstructure in the robust offline model of the process. The real-time control schemes will enable the ground breaking capabilities of the SLE process to create engine-ready net shape turbine components from raw powder material.

Materials intended for disposal of spent nuclear fuel require a particular combination of physical and chemical properties. The driving forces and mechanisms underlying the material’s behavior must be scientifically understood in order to enable modeling at the relevant time- and length-scales. The processes that determine the mechanical behavior of copper canisters and iron inserts, as well as the evolution of their mechanical properties, are strongly dependent on the properties of various defects in the bulk copper and iron alloys. The first part of the present thesis deals with precipitation in the cast iron insert. A nodular cast iron insert will be used as the inner container of the spent nuclear fuel. Precipitation is investigated by computing effective interaction energies for point defect pairs (solute–solute and vacancy–solute) in bcc iron using first-principles calculations. The main considered impurities in the iron matrix include 3sp (Si, P, S) and 3d (Cr, Mn, Ni, Cu) solute elements. By computing interaction energies possibility of formation of different second phase particles such as late blooming phases (LBPs) in the cast iron insert is evaluated. The second part is devoted to the fundamentals of dislocations and their role in plastic deformation of metals. Deformation of single-crystal copper under high strain rates is simulated by employing dislocation dynamics (DD) method to examine the effect of strain rate on mechanical properties as well as dislocation microstructure development. Creep deformation of copper canister at low temperatures is studied. The copper canister will be used in the long-term storage of spent nuclear fuel as the outer shell of the waste package to provide corrosion protection. A glide rate is derived based on the assumption that at low temperatures it is controlled by the climb rate of jogs on the dislocations. Using DD simulation creep deformation of copper at low temperatures is modeled by taking glide but not climb into account. Moreover, effective stresses acting on dislocations are computed using the data extracted from DD simulations. / <p>QC 20170428</p>

Four molecular germanates based on salicyl alcoholates, bis(dimethylammonium) tris[2-(oxidomethyl)phenolate(2-)]germanate (1), bis(dimethylammonium) tris[4-methyl-2-(oxidomethyl)phenolate(2-)]germanate (2), bis(dimethylammonium) tris[4-bromo-2-(oxidomethyl)phenolate(2-)]germanate (3) and dimethylammonium bis[2-tert-butyl-4-methyl-6-(oxidomethyl)phenolate(2-)][2-tert-butyl-4-methyl-6-(hydroxymethyl)phenolate(1-)]germanate (4), were synthesized and characterized including single crystal X-ray diffraction analysis. In the solid state, compounds 1 and 2 exhibit one-dimensional hydrogen bonded networks, whereas compound 4 forms separate ion pairs, which are connected by hydrogen bonds between the dimethylammonium and the germanate moieties. The potential of these compounds for thermally induced twin polymerization (TP) was studied. Germanate 1 was converted by TP to give a hybrid material (HM-1) composed of phenolic resin and germanium dioxide. Subsequent reduction with hydrogen provided a microporous composite containing crystalline germanium and carbon (Ge@C – C-1, germanium content ∼20%). Studies on C-1 as an anode material for Li-ion batteries revealed reversible capacities of ∼370 mA h gGe@C−1 at a current density up to 1384 mA g−1 without apparent fading for 500 cycles. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Le présent travail s’intéresse à l’électro-dépôt et à la caractérisation des nanofilms Pt/Pd(hkl) ainsi que leurs propriétés en relation avec le stockage d’hydrogène. Les effets de taille nanométrique, de l’épaisseur et de l’orientation cristallographique du substrat ont été étudiés.En comparant les films Pd/Pt(111) et Pd/Pt(100), des caractéristiques distinctes ont été observées aussi bien pour les courbes d’électro-dépôt que durant les caractérisations électrochimiques et par AFM ex situ. Les dépôts Pd/Pt(100) ont montré la présence d’un dépôt en sous tension jusqu’à deux couches atomiques, ce qui est assez inhabituel. Les films plus épais montrent la présence de pyramides à base carrée alignées sur l’orientation (100) du substrat. Au contraire, seule la première couche de Pd/Pt(111) se dépose en sous-tension et le dépôt présente un caractère pseudomorphe jusqu’à 10 couches complètes.L’absorption d’hydrogène dans les nanofilms de Pd/Pt(100) a été étudiée avec une méthode « classique » dans une solution d’acide sulfurique. Nous avons développé une nouvelle méthode recourant à une électrode tournante à ménisque suspendu pour mesurer l’insertion d’hydrogène dans les films les plus minces de Pd/Pt(111), où l’insertion d’hydrogène et le dégagement de H2(g) ne sont pas bien séparés.Les isothermes d’insertion d’hydrogène présentent des points communs entre les deux systèmes, comme la réduction du taux maximal d’insertion (H/Pd)max comparé au Pd massif, valeur qui décroît avec la réduction d’épaisseur. La largeur de la région biphasique décroît aussi avec la réduction d’épaisseur de film et présent une pente. Cette pente a été attribuée à la présence de sites d’insertion non-équivalents résultant des contraintes induites par le substrat. Cependant, pour Pd/Pt(100), la pente est moins prononcée et la valeur de (H/Pd)max décroît plus rapidement avec l’épaisseur. Sa valeur pour Pd5ML/Pt(100) est à peine supérieure au taux d’insertion αmax du Pd massif. / The present work focuses on the electro-deposition and characterization of Pd/Pt(hkl) nanofilms and on their properties concerning hydrogen storage. The effects of the nanometric size, of the thickness and of the substrate’s orientation have been studied.Comparing Pd/Pt(111) and Pd/Pt(100) films, distinct features were observed either in the electrodeposition curve or in the electrochemical and ex situ AFM characterizations. Pd/Pt(100) deposits have shown the presence of an UPD process up to two layers, which is a quite uncommon phenomenon. Thicker films show the presence of square based pyramids, following the substrate’s (100) orientation. On the contrary, only the first layer is Under Potentially Deposited in Pd/Pt(111) films and the deposit presents a pseudomorphic character up to about 10 complete layers.Hydrogen absorption into the Pd/Pt(100) nanofilms was studied following a “classical” method in sulphuric acid medium. We have developed a new method using the hanging meniscus rotating disk electrode (HMRDE) to measure the hydrogen insertion into ultra-thin Pd/Pt(111) films, where H insertion and HER (Hydrogen Evolution Reaction) are not well separated. The hydrogen insertion isotherms present some common points between the two studied systems, like smaller value of the maximum hydrogen insertion rate (H/Pd)max compared to bulk Pd, value which decreases with the decrease of the thickness. The two-phase region width decreases with film thickness as well and presents a slope. Such slope has been attribtued to the presence of non-equivalent insertion sites due to substrate induced constraints. Nevertheless, for Pd/Pt(100) the slope is less pronounced and (H/Pd)max value decreases more rapidly with thickness. Its value in correspondence of Pd5ML/Pt(100) is only slightly higher than the αmax insertion rate of bulk Pd.

Le travail a consisté, dans une première partie, à modéliser la dynamique des défauts ponctuels dans les mono-cristaux de silicium. Il s'est agi en premier lieu d'analyser en profondeur le modèle physique, pour introduire et comprendre le rôle de la thermodiffusion dans le modèle de transport-diffusion et recombinaison des interstitiels et des lacunes. Par une analyse asymptotique, nous sommes parvenus à prédire la composition du cristal en termes des densités de lacunes ou d'interstitiels. Nous avons également proposé un nouvel ensemble de paramètres matériels tenant compte de résultats d'expériences récentes sur la diffusivité des lacunes. Enfin, nous avons simulé numériquement le calcul des défauts ponctuels dans le procédé Czochralski de croissance de cristaux de silicium et l'avons validé par comparaison avec des résultats expérimentaux. Le travail principal dans cette thèse a consisté en l'élaboration d'une théorie mathématique permettant de décrire de manière rigoureuse la géométrie des dislocations dans les mono-cristaux. Par nature, ces défauts sont concentrés sur des lignes qui sont libres de former des réseaux complexes interagissant à leur tour avec les défauts ponctuels. Il s'est agi de proposer une théorie à l'échelle mésoscopique qui tienne compte à la fois de la multiformité des champs de déplacement et rotation tout en admettant que les effets non-élastiques soient concentrés dans la ligne. Les principaux champs intervenant dans cette théorie sont des densités de dislocations et de disclinations représentés par des tenseurs d'ordre 2 tenant compte à la fois de l'orientation de la ligne et des vecteurs de Frank et Burgers, qui sont des invariants caractérisant respectivement les défauts de rotation et de déplacement dans le cristal. Ces champs sont reliés à l'incompatibilité de la déformation élastique par l'intermédiaire de termes concentrés sur les lignes, qu'il a fallu décrire et formaliser dans un cadre mathématique rigoureux et cohérent. La description de la physique des dislocations a été rendue possible par l'application à la théorie des dislocations de certains nouveaux outils mathématiques tels, par exemple, la théorie des distributions, la théorie géométrique de la mesure, et la géométrie non-riemannienne. Enfin, l'homogénéisation de l'échelle mésoscopique vers l'échelle macroscopique des densités de dislocations, représentées par des tenseurs d'ordre 2, a permis de poser le problème à l'échelle du cristal, où les champs sont réguliers, obéissent à des lois de conservation, de constitution et d'évolution. Le travail de thèse s'est arrêté précisément au moment de modéliser l'échelle macroscopique, notamment les lois de constitution des densités de dislocations. / This thesis comprises two main parts and provides contributions to the fields of point- and line defects in single crystals. The point-defect transport, diffusion and recombination mechanisms are modeled in silicon crystals, whereas a theoretical approach is developped for the description of the geometry of dislocations. Therefore, plasticity, which is caused by the motion of dislocations, is not the topic of the present work. Dislocations are typical line-defects. Once generated during the growth of a silicon or other crystal, they can instantaneously multiply and generate dislocation networks, that render the material unusable for device manufacturing. We develop a theory to represent dislocated single crystals at the mesoscopic scale by considering concentrated effects along the dislocation line, as governed by the distribution theory combined with multiple-valued kinematic fields. Fundamental 2D identities relating the incompatibility tensor to the Frank and Burgers vectors are proved under global assumptions on the elastic strain, relying on the geometric measure theory, thereby giving rise to rigorous homogenisation from mesoscopic to macroscopic scale. The class of point-defects comprises the monoatomic defects which form the fundamental building blocks for grown-in defects in silicon crystals. A general model is build to conduct fully time-dependent and global simulations in order to predict the distribution of point-defects in a growing silicon crystal. Furthermore, the defect governing model is adapted in order to better agree with available measurements of self-interstitial and vacancy diffusion coefficients while respecting the V/G criterion, which characterises the interstitial-vacancy transition in the crystal. It is shown that introducing a thermal drift effect can facilitate the construction of a relevant model satisfying both conditions.