nÃo hà / AÃos elÃtricos de grÃo nÃo orientado sÃo amplamente utilizados na fabricaÃÃo de nÃcleos para motores elÃtricos, sendo o desempenho destes equipamentos afetado pela textura cristalogrÃfica presente nesses materiais. Jà o tamanho de grÃo interfere consideravelmente nas perdas magnÃticas. A textura cristalogrÃfica e o tamanho de grÃo sÃo extremamente influenciados pelo tratamento tÃrmico de recozimento realizado apÃs o processo de laminaÃÃo a frio para obtenÃÃo de tiras metÃlicas desses aÃos. O recozimento promove estados de recristalizaÃÃo na microestrutura do material e esses estados estÃo intimamente relacionados com a textura cristalogrÃfica. O objetivo deste trabalho à avaliar a influÃncia da recristalizaÃÃo no comportamento da textura cristalogrÃfica e das perdas magnÃticas por histerese de um aÃo elÃtrico de grÃo nÃo orientado com 1,28% Si que foi laminado a frio industrialmente com reduÃÃes de 50 e 70%. Amostras do material nas condiÃÃes laminado a frio, parcialmente recristalizadas a 580, 585, 590, 595, 600, 605, 610, 615 e 620ÂC e recozidas a 730ÂC por 12 horas (recozimento em caixa) foram analisadas quanto à microestrutura, textura cristalogrÃfica e perdas magnÃticas por histerese. O material tambÃm foi submetido a tratamentos tÃrmicos para crescimento de grÃo e estes tambÃm foram avaliados com respeito à microestrutura e a textura cristalogrÃfica. Os resultados mostraram o inÃcio da recristalizaÃÃo primÃria nas condiÃÃes parcialmente recristalizadas e os tratamentos tÃrmicos para crescimento de grÃo provocaram a ocorrÃncia de recristalizaÃÃo secundÃria. A textura cristalogrÃfica foi modificada pelas condiÃÃes parcialmente recristalizadas, pelo recozimento em caixa e pela recristalizaÃÃo secundÃria. Quanto Ãs perdas magnÃticas por histerese, o recozimento em caixa promoveu uma diminuiÃÃo destas. / Non-oriented electrical steels are widely used in the manufacture of cores for electric motors being the performance of this equipment affected by the presence of crystallographic texture in these materials. In other hand, the grain size considerably affects the magnetic losses. The crystallographic texture and grain size are greatly influenced by the annealing process performed after cold rolling of these steels. Annealing promotes recrystallization in the microstructure of the material which is closely related with the crystallographic texture. The objective of this study is to evaluate the influence of recrystallization on the evolution of crystallographic texture and hysteresis magnetic losses by in non-oriented grain electrical steel with 1.28% Si that was cold rolled with reductions of 50 and 70% in an industrial plant. Samples of the material in the conditions cold rolled and partially recrystallized at 580, 585, 590, 595, 600, 605, 610, 615 and 620ÂC and annealed at 730ÂC for 12 hours (box annealing) were analyzed in the aspects of microstructure, crystallographic texture and magnetic hysteresis losses. The material was also subjected to heat treatment for grain growth and they were also evaluated with respect to the microstructure and crystallographic texture. The results showed the evolution of primary recrystallization and also the microstructure and texture when the material is subjected to final heat treatment that promotes grain growth and secondary recrystallization. The crystallographic texture has changed in the process of primary recrystallization occurred during box annealing and also in the process of secondary recrystallization after heat treatment simulating the final processing of the material. The evaluation of hysteresis magnetic losses showed that the box annealing promoted a reduction of these.

O desgaste abrasivo de dois aços austeníticos ao manganês, materiais com grande utilização na mineração, foi estudado empregando metodologia multiescala (escalas: macro, meso e micro). Na macroescala foram estudados os mecanismos de dano e de desgaste de revestimento de britador utilizado em campo. Na mesoescala foram realizados ensaios de britador de mandíbula e de esclerometria linear. Na microescala o ensaio de esclerometria linear foi utilizado para avaliar os efeitos da camada encruada em campo e da orientação cristalográfica dos grãos austeníticos dos aços com 12 %Mn e 20 %Mn. As técnicas de caracterização utilizadas nesta pesquisa foram: macro e microdureza, nanodureza instrumentada, MO, MEV, DRX, EBSD, FIB e MET. A pesquisa foi dividida em três Capítulos, intitulados: \"Desgaste abrasivo dos aços austeníticos com 12 %Mn e 20 %Mn via ensaio de britador de mandíbula\"; \"Efeito do encruamento e da orientação cristalográfica no desgaste por riscamento dos aços austeníticos 12 %Mn e 20 %Mn\"; e \"Microestrutura da subsuperfície do aço austenítico com 12 %Mn deformado por desgaste abrasivo\". O primeiro Capítulo mostrou, a partir do ensaio de britador de mandíbulas (mesoescala), que o aço com 20 %Mn tem tendência de maior resistência ao desgaste que o aço com 12 %Mn. Este resultado foi obtido para a mandíbula fixa do britador, na qual a severidade de desgaste foi superior a mandíbula móvel, por apresentar microcorte e microsulcamento como micromecanismos predominantes, enquanto na mandíbula móvel o micromecanismo predominante foi a microendentação. No segundo Capítulo observou-se que o desgaste por riscamento (mesoescala e microescala) não depende do perfil de encruamento gerado em campo. Entretanto, foi identificado o efeito da orientação cristalográfica, planos (001), (111) e (101), no desgaste por riscamento dos aços com 12 %Mn e 20 %Mn. No último Capítulo a análise multiescala mostrou que a microestrutura deformada na subsuperfície sofre alterações semelhantes em diferentes intensidades. Nas três escalas de análise foram observadas uma camada com grãos ultrafinos (nanométricos), na subsuperfície, e uma de transição com maclas de deformação. A formação dos grãos ultrafinos foi associada à recristalização dinâmica por deformação plástica, na qual faz parte do mecanismo de auto reparação superficial. Além dos resultados apresentados, o desenvolvimento desta pesquisa de doutorado permitiu a elaboração de duas metodologias: i. análise do efeito da orientação cristalográfica no desgaste por microesclerometria; e ii. análise de microestrutura revelada por ataque iônico - FIB. / The abrasive wear of two manganese austenitic steels, materials broadly used in mining industry, was studied using multiscale methodology (scales: macro, meso and micro). In the macroscale the mechanisms of damage and wear of in-service crusher liner were studied. In the mesoscale, jaw crusher and linear scratch tests were performed. In the microscale the linear scratch test was used to evaluate the effects of the hardening layer and the crystallographic orientation of the austenitic grains of steels with 12 %Mn and 20 %Mn. The characterization techniques used in this research were: macro and microhardness, instrumented nanohardness, OM, MEV, DRX, EBSD, FIB and TEM. The research was divided into three chapters, entitled: \"Abrasive wear of steels with 12 %Mn and 20 %Mn via jaw crusher test\"; \"The effect of the in-service workhardening and crystallographic orientation on the micro-scratch wear of austenitic steels with 12 %Mn and 20 %Mn\"; and \"Subsurface microstructure of the deformed austenitic steel with 12 %Mn by abrasive wear\". The first chapter showed, from the jaw crusher tests (i.e. mesoscale), that the steel with 20 %Mn tends to be more wear resistant than the steel with 12 %Mn. This result was obtained to the fixed jaw crusher, in which the wear severity was superior to the movable jaw, since it presents microcutting and microploughing as predominant micromechanisms, whereas in the mobile jaw the predominant micromechanism was microendentation. In the second chapter, it was observed that scratch wear (i.e. meso and microscale) does not depend on the in-service work-hardening profile. However, it was identified the effect of crystallographic orientation, (001), (111) and (101) planes, on the scratch wear of the steels with 12% Mn and 20% Mn. In the last chapter, the multiscale analysis showed that the subsurface deformed microstructure changes with different intensities. At the three analysis scales, a layer with ultrafine grains was observed in the subsurface and mechanical twins. The formation of this layer, with nanometric grains, was associated with dynamic recrystallization by plastic deformation, in which it is part of the self healing effect. In addition to the results found, the development of this doctoral research allowed for the elaboration of two methodologies: i. Analysis of the effect of crystallographic orientation on the scratch wear; and ii. Microstructure analysis revealed by ion etching - FIB.

Fatias de rochas compreendendo granitóides, gnaisses bandados, anfibolitos, quartzitos e metapelitos formam um sistema imbricado situado na porção oeste do Lineamento Patos (Província Borborema, NE do Brasil). A estrutura situada no sul do estado do Ceará, inserida no Bloco Assaré, nesse momento ainda carece de estudos geológicos que permitam a sua melhor compreensão. Neste contexto, o presente trabalho foi realizado com o objetivo de trazer novos dados geocronológicos e estruturais para acrescentar no entendimento do duplex transcorrente. Datações de rochas situadas no interior das escamas imbricadas em zircões (U-Pb) via LA-ICP-MS indicam que o duplexé constituído por unidades (escamas) de idades diferentes. Gnaisses bandados, diques de anfibolito e metaultramáficas da unidade Granjeiro forneceram idades arqueanas (gnaisses: c. 2.8 Ga, LM10; c. 3.2 Ga, LM3; dique: c. 3.0 Ga, LM2). Idades siderianas e riacianas foram encontradas em gnaisses e anfibolitos a oeste de Cajazeiras (c. 2.4 Ga, LM1; c.2.4, LM13) e em augen gnaisses a sul de Cedro (c. 2.2 Ga, LM11), respectivamente. Essas sequencias do embasamento encontram-se em contato alóctone com metapelitos e quartzitos agrupados na Formação neoproterozoica Lavras da Mangabeira. Critérios cinemáticos derivados doestudo das microestruturas e das tramas cristalográficas de milonitos ricos em quartzo mostram que a sequência metassedimentar foi empurrada para nordeste. Eixos-c e eixos- de quartzo indicam a ativação de sistemas de deslizamento de alta temperatura durante o desenvolvimento da trama. Estimativas de temperaturas baseadas na abertura de ângulo da trama de eixos-c e em contatos suturados entre grãos de quartzo indicam que a deformação dúctil ocorreu entre 500 e 700 °C. A formação do duplex transcorrente, que constitui uma estrutura única na Província Borborema, possivelmente foi facilitada pela presença de rochas arqueanas que provavelmente se comportaram de forma mais rígida durante a deformação facilitando o cavalgamento oblíquo dos conjuntos litológicos. O arranjo estrutural das fatias imbricadas é portanto consistente com um duplextranscorrente compressivo induzido pela deformação cisalhante destral. / Slices of metaplutonic rocks, banded gneiss, amphibolites and metasedimentary sequences form a strike-slip duplex situated in the west portion of the Patos Lineament (Borborema Province, Northeastern Brazil). U-Pb (LA-ICP-MS) data in zircons from the imbricate slices indicate they are constituted by rocks of different ages. Banded gneiss, orthogneisses and metaultramafic dikes assembled in the Granjeiro Complex yielded Archean ages between 2.8 and 3.2 Ga. In contrast, biotite gneisses and amphibolites produced a Siderian (ca. 2.4 Ga) age and an augen gneiss apparently intrusive in the Siderian sequences yielded a Rhyacian (ca. 2.2 Ga) age. These basement sequences are in allochtonous contact with metapelites and quartzites grouped in the Lavras da Mangabeira Formation of Neoprotrozoic age. Kinematic criteria deduced from the study of the microstructures and crystallographic fabric of quartz-rich mylonites show that the metasedimentary sequence was thrusted to the northeast direction. Crystalligraphic c- and a- axis of quartz indicated that medium- to high temperature slip-systems were active during the fabric development. Temperature estimations based on the opening-angle of the c-axis fabric and the sutured contacts between quartz-quartz grains indicated that the ductile deformation occurred at 500 and 700°C. The development of the tectonic duplex was likely facilitated by the occurrence of Archean rocks involved in the shear deformation. They would have acted as a rigid (competent) material that induce the stacking of the sequences during the bulk dextral transcurrent deformation of the Patos Lineament.

Dans les instants qui suivent l'implantation d'ions hydrogène dans du silicium monocristallin à température ambiante, des défauts complexes se forment et une contrainte en compression apparaît dans les plans parallèles à la surface du wafer. L'évolution thermique de ce système au cours du recuit conduit à la co-précipitation d'atomes d'hydrogène et de lacunes de silicium sous la forme de cavités plates (platelets) localisées dans deux familles de plans. Ces platelets sont à l'origine d'un phénomène de fracture utilisé par l'industrie pour la fabrication de substrats SOI innovants et le mécanisme conduisant à leur formation doit être approfondi. Dans ce travail, nous avons tout d'abord décrit la formation, à température ambiante, des complexes résultants de la rencontre entre les défauts ponctuels initialement générés par l'implantation. Le modèle proposé dépend des concentrations et des diffusivités de ces défauts ponctuels ainsi que des énergies de formation des complexes considérés. Nous avons relié ces concentrations à la contrainte générée ainsi qu'à la déformation du cristal en résultant. Des mesures expérimentales de ces grandeurs nous ont permis de calibrer notre modèle et de proposer une explication quant à la réaction mécanique du silicium à l'implantation d'hydrogène. Nous avons ensuite calculé la variation de l'énergie libre de Gibbs du système consécutive à la nucléation d'un platelet. Dans un cristal non contraint, cette énergie ne dépend que de la famille de plans à laquelle appartient le platelet. Dans un système sous contrainte, nous montrons que cette énergie dépend également d'un terme décrivant le couplage entre cette contrainte et le champ de déformation généré par le platelet. Puisque ces énergies contrôlent les taux de nucléation respectifs des différents variants d'orientation des platelets, nous avons pu calibrer notre modèle à partir d'observations expérimentales par TEM des occurrences des différents variants, en fonction de l'amplitude et de la direction de la contrainte, c'est-à-dire en fonction de l'orientation des wafers et de la profondeur considérée. Les modèles proposés dans ce travail, bien qu'appliqués à l'implantation d'hydrogène dans le silicium, sont tout à fait génériques. Ils montrent comment contraintes et défauts interagissent en fin d'implantation et en tout début de recuit thermique. Ils devraient permettre d'optimiser le procédé industriel Smart Cut(tm) en imposant des conditions favorisant la formation de " platelets utiles " à la fracture, mais au-delà, de manipuler l'orientation de nano-précipités dans des matrices cristallines, ouvrant ainsi la voie à la fabrication contrôlée de nanostructures fonctionnelles. / Hydrogen implantation at room temperature into monocrystalline silicon leads to the formation of complex defects and also to the appearance of in-plane compressive stress. During annealing hydrogen atoms and vacancies co-precipitate into platelets lying on two types of habit planes. These platelets play a decisive role in the fracture of the material that can occur during further annealing and which is used for the manufacture of SOI wafers. Thus, their nucleation mechanism has to be well understood. First, we described the formation of complexes at room temperature following the encounters of point defects formed by ion implantation. In this model, the concentrations of the formed complexes depend only on their formation energies and on the concentrations and diffusivities of point defects. Furthermore, the concentrations of the different complexes were coupled to the stress and strain build-up. Using the experimentally measured strain, we could calibrate our model and explain the mechanical reaction of silicon to hydrogen implantation. In a second part, the variation of the free Gibbs energy of the system following the nucleation of a platelet was calculated. In an unstressed crystal, this energy only relies on the habit plane of the platelet. When the system is under stress, this energy also depends on a term coupling this stress and the strain field generated by the platelet. Because those energies control the nucleation rate of the platelets variants, we could calibrate our model using the TEM observations of the platelets occurrences, as function of the stress amplitude and direction, i.e. as function of the wafer orientation and the platelet depth location. The models developed here are generic and can be applied to a wide variety of systems. They show how stress and defects interact once implantation is over and at the beginning of annealing. These models are believed to be helpful to optimize the industrial Smart Cut(tm) process by favoring the occurrence of platelets "useful" for fracture but, going beyond, to manipulate the orientation of nanocrystals in a crystalline matrix paving the way to the fabrication of "functional" nanostructures.

Coxeter group, named after H.S.M. Coxeter, is an abstract group that admits a formal description in terms of mirror symmetries. It turns out that the finite Coxeter groups are precisely the finite Euclidean reflection groups. Coxeter studied these groups and classified all finite ones in 1935, however they were known as reflection groups until J. Tits coined the term Coxeter groups for them in the sixties. Finite crystallographic Coxeter groups, also known as finite Weyl groups, play a prominent role in many branches of mathematics like combinatorics, Lie theory, number theory, and geometry. The computational aspects of these groups are of great interests and play a very important role in representation theory. Since it’s enough to study only the irreducible class of groups in order to understand any Coxeter group, we discuss irreducible crystallographic Coxeter groups here. Our goal is to try to deal with some of the fundamental computational problems that arise in working with the structures such as Weyl groups, root system, Weyl characters. For the classical cases, especially type A, many of these problems are not very subtle and have been solved completely. However, these solutions often do not generalize. In this report, our emphasis is on algorithms which do not really depend on the classifications of root systems. The canonical example, we always keep in mind is E8. In chapter 1, we fix the notations and give some basic results which have been used in this report. In chapter 2, we explain algorithms to various Weyl group problems like membership problem; how to find the length of an element; how to check if two words in a Weyl group represent the same element or not; finding the coset representative for an element for a given parabolic subgroup; and list all the expressions possible for an element. In chapter 3, the main goal is to write an algorithm to compute the weight multiplicities of the irreducible representations using Freudenthal’s formula. For this, we first compute the positive roots and dominant weights for a given root system and then finally find the weight multiplicities. We argue this mathematically using the results given in chapter 1. The crystallographic hypothesis is unnecessary for much of what is discussed in chapter 2. In the last chapter, we give codes of the computer programs written in C++ which implement the algorithms described in the previous chapters in this report.

In the first article, the seismic properties for a suite of rocks along the West Cycladic Detachment System (Greece) are calculated, using Electron backscatter diffraction (EBSD) measurements and the minerals’ elastic stiffness tensors. Muscovite and glaucophane well defined crystallographic preferred orientation increases the seismic anisotropy. Maximum Pwave velocities have the same orientation as the Miocene extension and maximum S-wave anisotropy is subhorizontal, parallel with mineral alignment, suggesting strong radial anisotropy with a slow subvertical axis of symmetry. In the second article, teleseismic receiver functions are calculated for an array of stations in the Cyclades and decomposed into back-azimuth harmonics to visualise the variations in structure and anisotropy across the array. Synthetic receiver functions are modeled using the first order structural observations of seismic discontinuities and EBSD data. They indicate 5% of anisotropy with slow symmetry axis in the upper crust, and demonstrate the importance of rock textural constraints in seismic velocity profile interpretation.

Les composés intermétalliques à base de terres rares et de métaux de transition présentent des propriétés magnétiques intéressantes pour les applications technologiques (aimants permanents, enregistrement magnétique à haute densité, réfrigération magnétique…).Ce travail est dédié à l'étude des propriétés structurales, magnétiques et magnétocaloriques des composés Pr2Fe17 dérivant de la structure Th2Zn17. Les propriétés magnétiques intrinsèques recherchées pour des propriétés performantes de ces composés sont améliorées sous l'effet de la substitution (fer par aluminium et praséodyme par dysprosium) et/ou l'insertion d'un élément léger (carbone). Les nanomatériaux intermétalliques sont élaborés par broyage à haute énergie suivi de recuit, ce qui pourrait conduire à des phases hors équilibre thermodynamique. L'homogénéité des alliages a été systématiquement analysée par diffraction des rayons X suivi de l'affinement Rietveld et par microscopie électronique en transmission. Les résultats ont montré qu'on peut former la phase désirée monophasée en faisant un broyage suivi d'un recuit de 30 min au lieu d'un recuit de 7 jours pour les composés massifs. Ceci représente un gain de temps non négligeable. D'après les mesures magnétiques effectuées, tous les composés possèdent une transition de phase de second ordre. Leur température de Curie augmente avec le taux d'Al et de Dy alors que la variation d'entropie diminue légèrement. Par ailleurs, l'insertion d'atomes interstitiels tels que le carbone a été réalisée. On remarque une nette amélioration de la température de transition. Il ressort de cette étude que ces composés présentent un grand intérêt dans la recherche de futurs matériaux magnétocaloriques pour la réfrigération magnétique à température ambiante / The intermetallic compounds based on rare earth and transition metals present interesting magnetic properties for technological applications (permanent magnets, high density magnetic recording, magnetic refrigeration ...).This work is dedicated to the study of structural, magnetic and magnetocaloric of Pr2Fe17 compounds Th2Zn17-type structure. The intrinsic magnetic properties of these compounds are improved due to the substitution (iron and aluminum by praseodymium by dysprosium) and / or the insertion of a light element (carbon). Intermetallic nanomaterials are prepared by high energy milling and subsequent annealing, which could lead to non-equilibrium phases. The homogeneity of these alloys was checked by X-ray diffraction and by transmission electron microscopy. The results have showed that single-phase can be obtained by milling and annealed during 30 min instead of 7 days annealing for bulk compounds. This represents a considerable saving of time. From the magnetic measurements, all compounds exhibit a second order phase transition. Their Curie temperature increases with the rate of Al and Dy as the entropy change slightly decreases. Moreover, the insertion of interstitial atoms such as carbon was achieved. We notice a significant improvement of the transition temperature. It appears from this study that these compounds are of great interest in the search for future magnetocaloric materials for magnetic refrigeration at room temperature

2-Cys Prx compõem um grupo de enzimas antioxidantes homodiméricas que atuam na decomposição de hidroperóxidos utilizando uma cisteína reativa (cisteína peroxidásica - CysP). A alta reatividade da CysP é alcançada com o envolvimento de dois aminoácidos vicinais à CysP: uma treonina e uma arginina, que constituem a tríade catalítica. Após a decomposição do hidroperóxido, a CysP forma um dissulfeto intermolecular com um segundo resíduo de cisteína (cisteína de resolução - CysR), o qual é reduzido pela tiorredoxina (Trx). Durante o ciclo redox, estas enzimas sofrem alterações estruturais, mas os mecanismos envolvidos neste processo eram pouco compreendidos. Neste trabalho foi obtida a estrutura cristalográfica de Tsa1 de Saccharomyces cerevisiae, uma 2-Cys Prx. Através de abordagens envolvendo bioquímica e biologia molecular, foi verificada a importância de aminoácidos envolvidos na reatividade e em transições da estrutura terciária e quaternária. Por fim, foram realizados esforços para a determinação da estrutura cristalográfica de mutantes obtidos neste trabalho. / 2-Cys Prx constitute a group of homodimeric antioxidant enzymes that act in the decomposition of hydroperoxides using a reactive cysteine (peroxidase cysteine - CysP). The high reactivity of the CysP is achieved by the participation of two vicinal amino acids: a threonine and an arginine, which constitute the catalytic triad. After the decomposition of hydroperoxide, the CysP forms an intermolecular disulfide with a second cysteine residue (resolving cysteine - CysR), which is reduced by the thioredoxin (Trx). During the redox cycle, these enzymes undergo to changes in the structure, but the molecular mechanisms involved in this process were poorly understood. In this study we have obtained the crystallographic structure of the 2-Cys Prx enzyme Tsa1 from Saccharomyces cerevisiae. By means of biochemical and molecular biology approaches, the importance of amino acids involved in reactivity and structural transitions were determined. Finally, efforts have been performed to the determination of the crystallographic structures of mutant proteins obtained in this study.

The invention of the lithium-ion battery has revolutionized the passenger transportation field in recent years, and it has emerged as one of the state-of-the-art solutions to address greenhouse gases emission and air pollution issues. Layered oxide lithium-ion battery cathode materials have become commercially successful in the past few decades due to their high energy density, high power density, long cycle life, and low cost. Yet, with the increasing demand for battery performance, it is crucial to understand the material fading mechanisms further to improve layered oxide materials' performance. A heterogeneous redox reaction is a dominant fading mechanism, which limits the utilization percentage of a battery materials' redox capability and leads to adverse effects such as detrimental interfacial reactions, lattice oxygen release, and chemomechanical breakdown. Crystallographic defects, such as dislocations and grain boundaries, are rich in battery materials. These crystallographic defects change the local lithium-ion diffusivity and have a dramatic effect on the redox reactions. To date, there is still a knowledge gap on how various crystallographic defects affect electrochemistry at the microscopic scale. Herein, we adopted synchrotron-based diffraction, imaging, and spectroscopic techniques to systematically study the correlation between crystallographic defects and redox chemistries in the nanodomain. Our studies shed light on design principles of next-generation battery materials. In Chapter 1, we first provide a comprehensive background introduction on the battery chemistry at various length scales. We then introduce the heterogeneous redox reactions in layered oxide cathode materials, including a discussion on the impacts of heterogeneous redox reactions. Finally, we present the different categories of crystallographic defects in layered oxide materials and how these crystallographic defects affect electrochemical performance. In Chapter 2, we use LiCoO2, a representative layered oxide cathode material, as the material platform to quantify the categories and densities of various crystallographic defects. We then focus on geometrically necessary dislocations as they represent a major class of crystallographic defects in LiCoO2. Combining synchrotron-based X-ray fluorescence mapping, micro-diffraction, and spectroscopic techniques, we reveal that geometrically necessary dislocations can facilitate the charging reactions in LiCoO2 grains. Our study illustrates that the heterogeneous redox chemistries can be potentially mitigated by precisely controlling the defects. In Chapter 3, we systematically investigated how grain boundaries affect redox reactions. We reveal that grain boundaries can guide redox reactions in LiNixMnyCo1-x-yO2 (NMC) materials. Specifically, NMC materials with radially aligned grains have a more uniform charge distribution, less stress mismatch, and better cycling performance. NMC materials with randomly orientated grains have a more heterogeneous redox reaction. These heterogeneous redox reactions are related to the lattice strain mismatch and worse cycling performance. Our study emphasizes the importance of tuning grain orientations to achieve improved performance. Chapter 4 systematically investigated how the grain boundaries and crystallographic orientations affect the thermal stability of layered oxide cathode materials. Combining diffraction, spectroscopic, and imaging techniques, we reveal that a cathode materials' microstructure plays a significant role in determining the lattice oxygen release behavior and, therefore, determines cathode materials' thermal stability. Our study provides a fundamental understanding of how the grain boundaries and crystallographic orientations can be tuned to develop better cathode materials for the next-generation Li-ion batteries. Chapter 5 summarizes the contributions of our work and provides our perspective on future research directions. / Doctor of Philosophy / Lithium-ion battery technology has revolutionized the portable electronic device and electric vehicle markets in recent years. Yet, the performance of current lithium-ion batteries still cannot satisfy customer demands. To further improve battery performance, we need a deeper understanding of why battery materials degrade over long-term cycling. One of the fading mechanisms in lithium-ion batteries is heterogeneous redox reactions, i.e., charge or discharge reactions do not proceed at the same pace at different locations in the electrode materials. Herein, we utilize layered oxide cathode materials as an example to systematically investigate how crystallographic defects in the cathode materials lead to heterogeneous redox reactions. Our study indicates that crystallographic defects, such as geometrically necessary dislocations, contribute positively to the charging reaction of the cathode materials. We also unveil that the grain crystallographic orientations of the primary particles affect the redox reactions directly. By aligning the single grains in the radial direction, the volumetric-change-induced stress can be effectively mitigated to ensure prolonged cycling performance. Our study also points out that the single grain orientations are related to the thermal stability of the battery materials. To summarize, our studies provide new insights into the heterogeneous redox reactions in battery materials and offer critical material design criteria to improve battery performance further.

Na constante busca de novas estratégias para melhorar a atividade catalítica, foi que a começos do século passado, a síntese de nanopartículas de formato controlado, tornou-se em um dos acontecimentos que revolucionaram a abordagem catalítica da Química, criando assim a linha da nanociência, onde com a síntese de nanopartículas de formato ao nível nano, é possível controlar as propriedades catalíticas dos materiais a nível macroscópico. O presente trabalho apresenta, a síntese de nanopartículas de óxido cuproso (NPs-Cu2O) com faces cristalográficas controladas. Foi possível sintetizar estruturas cúbicas, esféricas, e octaédricas, sendo os cubos e octaedros os que possuem faces cristalográficas de tipo (100) e (111), respectivamente. Entretanto, as esferas possuem uma mistura entre ambas das faces. As propriedades catalíticas das NPs-Cu2O foram testadas eletroquimicamente mediante uma reação modelo de detecção de glicose. As NPs-Cu2O, foram sintetizadas em médio básico com cloreto de cobre (CuC12) como percursor, posteriormente com concentrações diferentes de cloridrato de hidroxilamina (NH2OHoHCI) foram obtidas NPs-Cu2O com estrutura cúbica, octaédrica e esférica. Posteriormente, foram imobilizadas numa superfície de eletrodo de carbono vítreo, mediante a técnica de casting. A oxidação catalítica da glicose, permitiu observar que o desempenho da estrutura cúbica fossesuperior, com uma sensibilidade de 442 ± 7 µA mM-1 cm-2, enquanto as estruturas esféricas e octaédricas foram de 165 ± 3 µA mM-1 cm-2 e 38 ± 1 µA mM-1 cm-2, respectivamente. Seguido as NPs-Cu2O, foram testadas na presença de Ácido Ascórbico (AA) e Ácido Úrico (UA), foi observado que os cubos possuem uma seletividade única, comparada com as outras estruturas. Dito comportamento foi estudado com Analise computacional (DFT), onde foi possível de observar que a distribuição entre átomos de Cobre e Oxigênio, determina a seletividade do material. Numa segunda etapa, para entender a importância da conservação estrutural e integridade morfológica, foram testadas as NPs-Cu2O, aos diferentes dias após de ser sintetizadas, observando claramente uma relação entre estrutura e atividade catalítico. Foi observado que nas estruturas cúbicas o deterioro foi maior em comparação com as outras estruturas, isto acompanhado mediante DFT, foi determinado que estrutura cúbica apresenta uma maior interação com o oxigênio, provocando assim, que a rápida transformação de Cu(I) para Cu(II), como CuO. Por último as NPs-Cu2O, foram testadas por espectroscopia de fotoelétrons excitados por raios X (XPS), este analise ajudou a compreender que o desempenho catalítico, não estava relacionado com a formação de Cu (III). Estes resultados foram apoiados pelos resultados obtidos pela espectroscopia de infravermelho in situ (FTIR), já que nessa análise foi possível de observar como o estabilizante (SDS), foi determinante em cada estrutura. / In the constant search for new strategies by advance of catalytic activities, was that at the beginning of the last century the synthesis of nanoparticles in a controlled format, became one of the events that revolutionized the catalytic approach of Chemistry, thus creating a line of nanoscience, where with the synthesis of nanoparticles of format at the nano level, it is possible to control catalytic properties of materiais at the macroscopic level. Consequently, the present work the synthesis of cuprous oxide nanoparticles (Cu2O-NPs), with crystallography faces welldefined. It was possible synthesize cubic, spherical and octahedral structure, the cubes and octahedrons being those having crystallographic faces of type (100) and (111), respectively. Meanwhile, the spheres have a mixture between both faces. The catalytic properties of Cu2O-NPs were electrochemically tested by a model glucose detection reaction. The Cu2O-NPs were synthetized in basic solution with cooper chlorate (CuCl2) like precursor, after with different concentration of hydroxylamine hydrochloride (NH2OH· HCl) were obtain cubic, spheres and octahedral structure. Posteriorly, were immobilized in a glassy carbon surface, through the technique of casting. The catalyst oxidation of glucose allowed observe that the performance of cubic structure was superior, with a sensibility of 442 ± 7 µA mM-1 cm-2, while the spheres and octahedral structure were 165 ± 3 µA mM-1 cm-2 e 38 ± 1 µA mM-1 cm-2, respectively. Following the Cu2O-NPs, they were tested in the presence of Ascorbic Acid (AA) and Uric Acid (UA), it was observed that the cubes have a unique selectivity compared to the other Cu2O-NPs structure. This behavior was studies with com putational analysis (DFT), where it was possible to observed that the distribution between copper and oxygen atoms determines the selectivity of material. In a second step, to understand the importance of structure conservation and morphological integrity, Cu2O-NPs were tested at different days after being synthesized, noting clearly a relation between structure and catalytic activity. It was observed that cubic structure the deterioration was greater in comparation with the other structures, this being accompanied by DFT, it was determinate that cubic structure show a greater interaction with the oxygen, thus provoking that rapid transformation of Cu (I) to Cu(II), like CuO. Finally, the Cu2O-NPs were tested by x-ray excited photoelectron spectroscopy (XPS), this analysis helped to understand the catalytic activity was not related to Cu (III) formation. These results were supported by those obtained by in situ (FTIR), since in this analysis it was possible to observe how the stabilizer (SDS) was determinant in each structure.