La déformation plastique du monocristaI de glace se produit essentiellement par glissement de dislocations dans les plans de base. Le glissement sur d'autres systèmes ou une éventuelle montée de dislocations basales limite la vitesse de déformation de la glace polycristalline. Dans les glaces des calottes polaires, une orientation préferentielle des axes c se développe au cours de la déformation, induisant une forte anisotropie viscoplastique. Un modèle auto-cohérent viscoplastique (VPSC) est utilisé pour calculer le comportement mécanique de la glace polycristalline et le développement des textures. Les résultats sont comparés à ceux du modèle à contraintes uniformes (borne inférieure) et à déformations uniformes (borne supérieure). Dans les modèles, il est supposé que le monocristal de glace se déforme par glissement basal, prismatique, et pyramidal. La résistance des systèmes de glissement d'un grain in-situ est déterminée à partir de résultats d'essais mécaniques sur des échantillons polycristallins fortement anisotropes. D'après le modèle VPSC, le comportement d'un grain in-situ est semblable à celui d'un monocristal isolé. Ce modèle reproduit parfaitement le comportement expérimental des glaces polycristallines anisotropes. Lorsqu'un polycristal est déformé de telle manière à ce que le glissement basal soit difficilement activé, la direction de la vitesse de déformation est très sensible à la direction de la contrainte, appliquée. De telles conditions de déformation devraient se retrouver dans le voisinage des dômes des calottes polaires. Dans les couches de surface des calottes polaires (zone de grossissement de grains), le modèle VPSC permet d'obtenir une bonne estimation du développement des textures. Dans les glaces plus profondes, on montre que la recristallisation par rotation a une influence significative sur le développement des textures. Une série d'essais mécaniques en laboratoire indique une tendance au comportement newtonien sous de très faibles contraintes.

Au cours d'une irradiation neutronique à long-terme dans les Réacteurs à Eau Pressurisée (REPs), une modification importante du comportement mécanique des matériaux utilisés dans les internes de cuve (composés des aciers inoxydables austénitiques de la série 300) est observée, y compris un durcissement et un adoucissement induit par irradiation, une perte de la ductilité et de la ténacité. Jusqu'à présent, beaucoup efforts ont été contribués pour identifier les effets d'irradiation sur l'évolution microstructurale du matériau (dislocations, boucles de Frank, cavités, ségrégation, etc.). Le gonflement induit par irradiation, considéré comme un facteur limitant la durée de fonctionnement des réacteurs, pourrait modifier les propriétés mécaniques des matériaux (plasticité, ténacité, etc), même conduire à une distorsion des structures du fait des modifications dimensionnelles entre les différentes composantes.L'objectif principal de ce travail de thèse est d'étudier qualitativement l'influence de l'effet du gonflement sur le comportement mécanique des matériaux irradiés. Un modèle micromécanique constitutif en grandes déformations basé sur les évolutions de la densité de dislocations et de défauts d'irradiation (boucles de Frank) est développé et implémenté dans les codes de calcul éléments finis ZéBuLoN et Cast3M. Les simulations numériques sont réalisées pour calculer les propriétés mécaniques d'un agrégat polycristallin. Par ailleurs, la technique d'homogénéisation est appliquée pour développer un modèle de type Gurson. Les simulations d'une cellule poreuse sont utilisés pour étudier le comportement mécanique des monocristaux poreux, en tenant compte des différents effets de la triaxialité, de la porosité et de l'orientation cristallographique, afin d'étudier l'effet de la présence des cavités sur la plasticité et la rugosité du matériau irradié à l'échelle polycristallin.

Cette thèse vise à trouver des approches possibles pour l’amélioration des propriétés électromécaniques de monocristaux piézoélectriques à base de KNN. La TSSG et la SSSG sont entreprises afin de faire croître des monocristaux La conclusion de l'aspect de croissance cristalline est: (1) Pour chaque élément pris individuellement, leurs coefficients de ségrégation reposent fortement sur leurs concentrations initiales dans la solution liquide. (2) La compétition entre éléments occupant le même site du réseau est démontrée. (3) Le très faible coefficient de ségrégation de Li dans la matrice KNN est responsable de l'apparition d'une phase secondaire présentant la structure bronze de tungstène quadratique. (4) Les régions optiquement laiteuses observées dans les monocristaux diminuent la réponse électrique et peuvent être réduites par traitement thermique et refroidissement lent. Dans la deuxième partie, nous avons utilisé trois approches pour améliorer le comportement piézo/ferroélectrique des monocristaux à base de KNN. La Ta ou Sb substitution indique qu'une réponse électromécanique améliorée est obtenue lorsque la transition orthorhombique-quadratique est à proximité de la température ambiante. Le traitement thermique sous atmosphère d'O2 pur a conduit au doublement de la valeur du coefficient piézoélectrique et des paramètres ferroélectriques d'un monocristal de (K,Na,Li) (Ta,Nb,Sb)O3. Son coefficient piézoélectrique à la température ambiante, qui constitue un record mondial à l’heure actuelle vis-à-vis de ce qui est reporté dans la littérature internationale, vaut 732 pC/N. La troisième approche consiste au dopage des monocristaux de (K,Na,Li)(Ta,Nb)O3 avec Mn. / The thesis aims to find possible approaches for improved electromechanical properties in KNN-based piezoelectric single crystals. Both submerged-seed and top-seeded solution growth techniques were employed to produce single crystals. Conclusions from the crystal growth aspect are: (i) For individual elements, segregation coefficients highly rely on the initial concentration in the liquid solution. (ii) A competition between elements occupied on the same lattice site was found. (iii) The very low Li segregation coefficient in the KNN matrix is responsible for the occurrence of a secondary phase with the tetragonal tungsten bronze structure. (iv) Observed optically-cloudy regions in as-grown crystals decrease the electrical response and can be reduced by thermal treatment with slow cooling. In the second part, we used three approaches to enhance the piezoelectric and ferroelectric behavior of KNN-based single crystals. Ta or Sb substitutions indicates that enhanced electromechanical response is achieved when the orthorhombic-tetragonal phase transition is near room temperature. Thermal treatment in pure O2 atmosphere resulted in a twofold increase of the piezoelectric coefficient and ferroelectric parameters of a (K,Na,Li)(Ta,Nb,Sb)O3 single crystal. The highest room-temperature piezoelectric coefficient in annealed KNN-based single crystals of 732 pC/N was obtained. The third approach, doping with Mn ions in (K,Na,Li)(Ta,Nb)O3 single crystals, is also presented.

Les solutions solides appartenant au système quasi-ternaire BaTiO3-CaTiO3-BaZrO3 (BCTZ) sont des candidates prometteuses pour les piézoélectriques sans plomb. Ce travail de thèse expérimental est consacré à la cristallogenèse et à la caractérisation de différents monocristaux dans le système BCTZ : BaZrO3, CaTiO3 ainsi que les solutions solides Ba1-xCaxTi1-yZryO3 présentant des teneurs en zirconium (Zr) et en calcium (Ca) proches de celles de la composition Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT) où les performances piézoélectriques sont exacerbées.Les monocristaux de CaTiO3 et de BaZrO3 ont été obtenus à la fois depuis une solution à haute température par la méthode du flux et à partir de leur phase fondue par la technique de la zone flottante optique. Dans le cas de CaTiO3 obtenu dans un four à image à 1975°C, l'aluminium (Al), le magnésium (Mg) et le baryum (Ba) ont été détectés comme étant les principales impuretés. Les spectres Raman de CaTiO3 sont en bon accord avec les spectres référencés dans la littérature. La croissance cristalline de BaZrO3 est beaucoup plus difficile à cause de son point de fusion très élevé (2700°C). Le flux BaB2O4 a été utilisé avec succès pour faire croitre des cristaux d’environ 150-200μm à 1350°C, soit à la moitié de son point de fusion. Des boules de BaZrO3 de taille centimétrique ont également été obtenues à partir de la phase fondue en four à image. Les impuretés majoritaires telles le strontium (Sr), l’hafnium (Hf), le calcium (Ca) et le titane (Ti) ont été détectées par GDMS et SIMS dans une gamme de concertation atomique de 0.3-0.5%. L’énergie de gap optique est d'environ 4,8 eV et souligne la grande qualité des cristaux de BaZrO3 obtenus en four à image. Les propriétés diélectriques à basse température de BaZrO3 confirment l'absence de transition de phase structurelle. Les études de Raman révèlent que même si BaZrO3 n'a pas de transition de phase à basse température, il présente une transition de phase cubique-quadratique sous haute pression à 11GPa à température ambiante.Dans la deuxième partie de cette thèse, des monocristaux centimétriques de BCTZ ont été obtenus avec succès par la croissance en flux. Les profils de concentrations en Ca et Zr le long des boules indiquent que leurs coefficients effectifs de ségrégation dépendent fortement de leur concentration initiale dans la solution liquide. Ceux-ci évoluent considérablement au cours du processus de cristallogenèse, rendant ainsi la croissance de BCTZ très délicate en vue d’obtenir des compositions constantes et proches de celles de la région de convergence de phases. De plus, une décomposition spinodale a été mise en évidence, indiquant la coexistence de deux solutions solides de compositions proches au sein des cristaux de BCTZ. Les propriétés diélectriques et piézoélectriques des cristaux obtenus ont été déterminées et présentent des caractéristiques allant du ferroélectrique classique au relaxeur. Les mesures diélectriques montrent notamment une double boucle d'hystérésis (PE) anormale qui disparaît après polarisation. / Solid solutions belonging to BaZrO3–BaTiO3–CaTiO3 (BCTZ) pseudo-ternary system are promising candidates for lead-free piezoelectrics. This thesis aims at growing and characterizing various single crystals of the BCTZ system: the end members BaZrO3 and CaTiO3 as well as Ba1-xCaxTi1-yZryO3 solid solution compounds with zirconium (Zr) and calcium (Ca) contents close to Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 composition (BZT-50BCT) where high piezoelectric performances are expected.CaTiO3 and BaZrO3 single crystals were both grown from high temperature solution by the flux method and from the melt by the optical floating zone technique. In the case of CaTiO3 grown with a mirror furnace at 1975°C, aluminum (Al), magnesium (Mg) and barium (Ba) as main impurities were detected. The Raman spectra of CaTiO3 are in good agreement with the spectra referenced in the literature. The growth of BaZrO3 was more challenging because of its very high melting point (2700°C). BaB2O4 flux was successfully used to produce 150-200 μm-sized BaZrO3 crystals at half its melting point (1350°C) and bulk centimeter-sized BaZrO3 boules were grown from the melt. Sr, Hf, Ca and Ti were detected by GDMS and SIMS as main impurities in the range of 0.3-0.5 at.%. The optical band gap is found to be ~4.8 eV and indicates the high quality of the BaZrO3 crystals grown with mirror furnace. Low temperature dielectric properties of BaZrO3 are displayed and confirmed the absence of structural phase transition. Raman investigations reveal that even though BaZrO3 does not have any phase transition at low temperatures, it exhibits a high-pressure phase transition from cubic to tetragonal at 11GPa at room temperature.In the second part, BCTZ centimeter-sized single crystals have been successfully grown by the top seeded solution growth technique. Ca and Zr content profiles throughout the as-grown boules indicate that their effective segregation coefficients are highly dependent on their initial concentration in the liquid solution. Concentrations evolve substantially during the crystal growth, making the BCTZ crystal growth a tricky issue when a narrow compositions range is targeted, as in the vicinity of the phase convergence region. Furthermore, spinodal decomposition was observed, indicating the coexistence of two solid solutions with close compositions in BCTZ crystals. Dielectric and piezoelectric properties were measured for some crystals, which were found to display a variety of behavior form relaxor to pure ferroelectric. In addition, an abnormal double-like PE hysteresis loop was observed, that was associated to an irreversible effect disappearing upon poling.

Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2016-01-15T17:06:54Z No. of bitstreams: 2 Dissertação - Rosane de Paula Castro - 2012.pdf: 7116126 bytes, checksum: d96286a63399d5f5187348a56b34a414 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-01-18T09:12:08Z (GMT) No. of bitstreams: 2 Dissertação - Rosane de Paula Castro - 2012.pdf: 7116126 bytes, checksum: d96286a63399d5f5187348a56b34a414 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-01-18T09:12:08Z (GMT). No. of bitstreams: 2 Dissertação - Rosane de Paula Castro - 2012.pdf: 7116126 bytes, checksum: d96286a63399d5f5187348a56b34a414 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2012-03-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work will be done initially, a review of the fundamentals of crystallography, besides the description of Direct Methods, commonly used in structural determination of small molecules, and the process of refinement of the obtained structure. The techniques for crystal growth will be presented and also a discussion about the process of data collection in the CAD4 diffractometer. Next, the process of obtaining single crystals and the crystallographic analysis of five novel compounds, which were synthesized by the Laborat´orio de Avaliac¸ ˜ao e S´ıntese de Substˆancias Bioativas (LASSBio) of Universidade Federal do Rio de Janeiro (UFRJ), are presented. These compounds are analogues of drugs, derivatives of N-phenylpiperazine and N-acylhydrazones, fragments that have important biological activities. The crystallographic structures of the following derivatives of N-phenylpiperazine were elucidated : LASSBio-1597, very active as anti-inflammatory, and an inclusion complex of the antipsychotic prototype, LASSBio-579, a dopamine receptor agonist, in β- cyclodextrin. The other compounds elucidated by X-ray crystallography are the N-acylhydrazones derivatives LASSBio-1606 analogue of Piroxicam, and compounds LASSBio-1586 polymorph I and LASSBio-1586 polymorph II , combretastatin-A4 analogue having potent anti-cancer activity, whose crystallographic analysis aimed to verify the existence of polymorphism suggested by DSC analysis (Differential scanning calorimetry). / Neste trabalho será feita, inicialmente, uma revisão dos fundamentos de cristalografia, além da descrição dos Métodos Diretos, correntemente utilizados na determinação estrutural de pequenas moléculas, e do processo de refinamento da estrutura obtida. Serão apresentadas técnicas de crescimento de cristais e, também, uma discussão sobre o processo de coleta de dados no Difratômetro CAD4. Posteriormente, serão apresentados o processo de obtenção dos monocristais e as análises cristalográficas de cinco compostos inéditos, que foram sintetizados pelo Laboratório de Avaliação e Síıntese de Substâncias Bioativas (LASSBio) da Universidade Federal do Rio de Janeiro (UFRJ). Estes compostos são análogos de fármacos, derivados de N-fenilpiperazina e de N-acilidrazona, fragmentos que apresentam importantes atividades biológicas. Foram elucidadas as estruturas cristalográficas dos seguintes derivados de N-fenilpiperazina: LASSBio-1597, bastante ativo como antiinflamatório, e o complexo de inclusão do protótipo antipsicótico, LASSBio-579, um agonista do receptor de dopamina, em β-ciclodextrina. Os outros compostos elucidados por cristalografia de raios X foram os derivados de N-acilidrazona LASSBio-1606, análogo do medicamento Piroxicam, e os compostos LASSBio-1586 polimorfo I e LASSBio-1586 polimorfo II, análogos da Combretastatina - A4 com potente atividade citotóxica tendo aplicações no tratamento de câncer, cuja análise cristalográfica teve como objetivo verificar a existência do polimorfismo sugerido pela análise de DSC (Differential scanning calorimetry).

Os radicais nitróxidos tem sido muito utilizados em estudos de sistemas biológicos através do método de marcagem de spin. Apesar do grande número de publicações sobre aplicações, o número de estudos das propriedades intrínsecas dos nitróxidos ê bem reduzido. A importância de tais estudos é grande uma vez que o estudo de um sistema simples permite avaliar e interpretar os resultados dos sistemas biológicos, geralmente mais complicados Assim no presente trabalho estudou-se o espectro do RPE do 4-hidroxi-2,2,6,6-tetrametil piperidina-1 oxil (I) introduzido como impureza na sua matriz diamagnética 4-hidroxi-2,2,6,6-tetrametilpiperidina (II). Este processo de dopagem muito utilizado em física do estado sólido permitiu a determinação dos tensores g e A. Os valores obtidos gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, e A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G, encontram-se dentro do esperado sendo que o valor de go = 2.0061 e Ao = 15.8 G evidencia a interação do fragmento N-O com ponte de hidrogênio (de hidroxila na posição 4 de uma molécula vizinha). A existência de dois centros paramagnéticos inequivalentes é interpretada corno devido a presença de duas possíveis conformações do fragmento N-O. As larguras das linhas de RPE observadas são grandes e em certas orientações do campo magnético ocorre o desdobramento da transição eletrônica num dubleto devido a interação com o hidrogênio da hidroxiIa que faz ponte com o N-O. A temperatura de cerca de -140&#176C e observada uma mudança sensível nos espectros de RPE evidenciando a desaparição da estrutura hiperfina na região de Axx e Ayy. Esta mudança está relacionada com o congelamento da rotação dos grupos metila afetando assim a interação dos prótons destes grupos com o elétron do fragmento N-O. O sistema estudado parece ser extremamente interessante do ponto de vista do estudo de influência de prótons na relaxação eletrônica do radical nitroxido. É evidenciada a forte dependência das propriedades paramagnéticas do nitróxido em relação à estrutura da vizinhança do fragmento N-O. / Nitroxide radicals are being used in many studies of biological systems through the spin label method. Despite the great number of publications involving the application of nitroxides only a reduced number of work s about nitroxides themselves is known. These studies are important because the knowledge of the properties of simple systems could be used in the interpretation of results in biological systems, normally mare complicated. In the present work the EPR spectra of 4-hydraxy-2,2,6,6-tetramethyl piperidine-l oxyl (I) introduced as impurity in the diamagnetic matrix of 4-hidraxy-2,2,6,6-tetramethyl piperidine (II) were studied. This process commonly used in solid state physics made it possible the determination of the g and A tensors. The values obtained : gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, and A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G are typical for nitroxides. The mean values go = 2.0061 and Ao 15.8G are consistent with the presence af hydrogen bond to the N-O fragment (this bond is made with the proton of a hydroxyl in position 4 of a neighbour molecule). The existence of two magnetically inequivalent centers is interpreted so that two different conformations for the N-O fragment are possible. The line widths of the EPR lines are quite great and for some orientations of the magnetic field a splitting of the electronic transition in to a dublet occur. This splitting is due to the interaction of the electron in the N-Q fragment with the hydroxyl hydrogen which is bonded to the nitroxide group. At a temperature around -140&#176C a change in the EPR spectra is observed, when the hyperfine nitrogen structure in the region of A and A disappear. This change x y is related to the freezing of the rotation of the methyl groups affecting the interaction of the protons of these groups with the electron in the N-O. The system studied in the present work seems to be very interesting from the point of view of the influence of the protons in the electronic relaxation in the nitroxide radical. ln this context the strong dependency of the properties of the nitroxide relative to the structure of the neighbouring of the N-O fragment become evident.

Résumé du travail L’étude des modifications de surfaces, et plus particulièrement des matériaux d’électrodes est un domaine en plein essor. Les modifications d’électrodes par voie organique ont des applications potentielles dans des domaines aussi variés que l’inhibition de la corrosion, l’électronique moléculaire, l’optoélectronique ou encore les biosenseurs. Dans ce travail, nous nous sommes intéressés à l’électrode d’Au (111) modifiée par du 2-mercaptobenzimidazole. Dans un premier temps, l’adsorption du MBI sur électrode d’Au (111) sous contrôle du potentiel a été examinée par des mesures de capacité, de voltampérométrie cyclique, de chronocoulométrie et de spectroscopie SNIFTIR in situ. Les mesures de capacité révèlent qu’en milieu neutre, la molécule de MBI s’adsorbe en un film compact à des potentiels supérieurs à -0,3 V (vs. ECS). En deçà de cette valeur, le film se dilue progressivement lorsque le potentiel est rendu plus négatif, jusqu’à une valeur de -0,9 V où les molécules de MBI sont totalement désorbées de la surface. La morphologie des voltampérogrammes subit des variations significatives au cours du temps. Ces changements montrent que l’adsorption du MBI s’accompagne d’une levée de reconstruction de la surface, qui passe d’une structure initiale (√3 x 22) à une structure (1 x 1). Une estimation de la quantité de MBI adsorbée est obtenue par intégration des courbes de densité de courant. La courbe de densité de charge interfaciale a été extraite des mesures de chronocoulométrie. Cette courbe de densité de charge fournit des informations quant à l’évolution de l’excès superficiel en fonction du potentiel. La qualité des spectres infrarouges relevés in situ nous a permis d’effectuer des analyses qualitatives et quantitatives. Celles-ci montrent une bonne corrélation avec les résultats électrochimiques et apportent une signature moléculaire du film adsorbé et des espèces issues de sa désorption. Des calculs basés sur la Théorie de la Fonctionnelle de la Densité (DFT) ont permis une bonne interprétation des spectres infrarouges du MBI et de certains de ses dérivés. En outre, nous avons pu déterminer l’orientation des molécules à la surface, et montré que celle-ci varie peu avec le potentiel. Dans un second temps, nous nous sommes focalisés sur les propriétés de la monocouche auto-assemblée de MBI sur électrode d’Au (111), déterminées par voltampérométrie cyclique et spectroscopie infrarouge in situ. La monocouche est stable lorsque le potentiel est maintenu dans un domaine d’environ 800 mV. La monocouche auto-assemblée de MBI subit un processus de désorption réductive, influencé par le temps d’immersion de l’électrode dans la solution de surfactant ainsi que par le pH du milieu. Deux mécanismes de désorption réductive sont proposés, l’un valable en milieu neutre et basique, l’autre en milieu acide. Les résultats des mesures de spectroscopie infrarouge in situ apportent une preuve moléculaire de la validité des mécanismes proposés sur base des résultats électrochimiques. Un rapide examen des potentialités de cette monocouche a été réalisé à l’aide de réactions sondes. / Abstract Studies on surface modifications, and particularly of electrode material, are a growing field of interest. Organic modifications of electrode surfaces have potential applications in domains such as corrosion inhibition, molecular electronics, optoelectronics or biosensors. In the present work, we focussed on the modification of Au(111) electrodes by 2-mercaptobenzimidazole (MBI). In the first part, the adsorption, under potential control, of the MBI molecule onto the Au(111) electrode was studied by means of capacitance measurements, cyclic voltammetry, chronocoulometry and in-situ SNIFTIR spectroscopy. Capacitance measurements indicate that in neutral solution, the MBI molecule is adsorbed as a compact film at potentials higher than -0.3 V (vs. SCE). Below this value, the film becomes progressively less dense when the potential is made more negative, until a value of -0.9 V where MBI molecules are totally desorbed from the surface. The shape of the voltammograms evolves significantly with time. These changes show that a lift of the surface reconstruction occurs concomitantly to the adsorption of MBI. The initial (√3 x 22) reconstructed structure is lifted to the (1 x 1) unreconstructed one. The amount of adsorbed MBI is estimated by integration of the current density curves. The interfacial charge density curve was obtained by chronocoulometry measurements. This curve provides useful data regarding the evolution of the surface concentration with the potential. The quality of the infrared spectra obtained in situ allowed us to perform quantitative as well as qualitative analyses of the results. These analyses show a good correlation with the electrochemical results and provide molecular information on the adsorbed layer and on the species formed during the desorption process. Density Functional Theory (DFT) calculations were helpful in the interpretation of the infrared spectra of MBI and some of its derivatives. Additionally, we were able to determine the orientation of the molecules on the surface, and demonstrated that this orientation is slightly affected by the potential. In the second part of the work, we investigated the properties of the self-assembled monolayer of MBI on Au(111) electrode by cyclic voltammetry and in situ infrared spectroscopy. The monolayer is stable within an 800 mV potential range. The self-assembled monolayer undergoes a reductive desorption process, which is affected by the pH of the medium and by the immersion time of the electrode into the surfactant solution. Two mechanisms were proposed for the reductive desorption, one being valid in neutral and basic media, the other in acidic conditions. The in situ infrared spectroscopic results provide molecular evidences supporting the mechanisms proposed on an electrochemical basis. An exploratory examination of the potentialities of the monolayer is made by means of electrochemical probe reactions.

Realizamos medidas de tempos de relaxação de centros F em cristais de KCN, pela técnica de saturação do sinal de absorção por pulsos de microonda. Observamos um comportamento não exponencial para a recuperação da magnetização da amostra ap6so pulso. Este fato deve-se ao efeito combinado de relaxação cruzada ou difusão da magnetização pelo espectro de absorção, juntamente com a relaxação spin-rede. Medidas à 4,2 °K e 1,8 °K fornecem indícios que, ap6s algum tempo, apenas a relaxação spin-rede sobrexiste. O modelo teórico baseado na modulação da interação hiperfina e no processo direto fornece tempos menores que os obtidos experimentalmente. Isto deve-se à formação de conglomerados de centros. Também elaboramos um modelo levando em conta processo Raman, para prever tempos de relaxação spin-rede a temperaturas mais elevadas. / We measure the spin-lattice relaxation time of F centers in KCN at 1.8 and 4.2 K using the saturation recovery technique. The observed recovery is non exponential. This result is interpreted in terms of the combined effect of cross-relaxation and spin lattice relaxation. The values obtained for T1 (- sec) are found to be shorter than those calculated theoretically. This discrepancy is throught to arise from the presence of clusters. The characteristic time found from the initial part of recovery is found to be -6 sec in agreement with that found in KC for the recovery of a hole burnt in the resonance line (45). Finally the value of T1 was calculated for the Raman processes at high temperature and compared with known results.

No presente trabalho foram estudados os espectros de RPE de um radical nitróxido, 4-hidroxi-2,2,6,6-tetrametilpiperidina-l-oxil (TEMPOL, 11), introduzido como impureza em uma matriz diamagnética, 4-hidroxi-2,2,6,6-tetrametilpiperidina (I), de estrutura conhecida. O uso do radical deuterado, 4-hidroxi-2,2,6,6 -tetrametilpiperidina-d17-l-oxil (PD-TEMPOL, 111) mostrou um aumento considerável na resolução dos espectros para a maioria das orientações do campo magnético. A interação do grupo paramagnético N-O com os prótons vizinhos foram estudadas e os tensores superhiperfinos de dois prótons fortemente acoplados foram determinados. Um desses prótons forma ponte de hidrogênio com o grupo N-O e a distância estimada é 2,09ª&#176. Os autovalores do tensor são: -5,2; 5,4 e -5,1 gauss. O segundo próton está mais distanciado do radical e provavelmente não forma ponte com o radical. Os valores nas direções principais são: 2,0; -1,7;e -2,7 gauss. Com a finalidade de estudar o envolvimento dos prótons na relação eletrônica dos radicais foram estimados os tempos de relaxação T1 e T2 no intervalo de temperatura de -160 a 25&#176C através do método de saturação continua. Foram obtidos os valores em diversas orientações para os radicais protonado (II) e deuterado - (III) para compará-los. Os valores de T2 obtidos são praticamente constante no intervalo de temperatura onde foram medidos e sistematicamente são maiores para o radical deuterado. O tempo de relaxação spin-rede, T1 é dependente da orientação para ambos os radicais. Em geral é obtida urna dependência linear de T1-1 versus T que foi explicada considerando um mecanismo de relaxação por tunelamento dos protons vizinhos entre dois poços de potenciais. Para o radical protonado é observada uma descontinuidade na curva de T1-1 versu T na região de -60&#176C; para o radical deuterado - isto é observado somente para algumas orientações. Este comporta mento poderia ser explicado como devido o congelamento da vibração das pontes de hidrogênio em torno desta temperatura. Um alagamento das linhas de RPE é observado para muitas orientações a partir de -100D&#176C que foi interpretado como devido o congelamento da rotação dos grupos metilas, do radical no caso (II) e da matriz no caso (I) / In the present work the ESR spectra of a nitroxide radical, 4-hydroxi-2,2,6,6-tetramethylpiperidine-l-oxyl (TANOL, lI), introduced as impurity in a diamagnetic host, 4-hydroxi-2, 2,6,6-tetramethylpiperidine (1), of know structure, has been investigated. The use of the deuterated radical, 4-hydroxi-2,2, 6,6-tetramethylpiperidine-d17-1-oxyl (PD-TANOL, 111) showed an improved resolution in the ESR spectra for most orientations of the magnetic field. The interactions of protons in the neighbourhood of the paramagnetic group N-O were studied and the superhyperfine tensors for the two strongly compled protons were determined one of these protons is hydrogen bonded to the N-O and the distance is estimated to be 2,09ª&#176. The superhyperfine tensor has principal values -5.2; +5.4; -5.1 gauss. The second proton is further away from the electron and probably is not hydrogen bonded. The principal values for this proton are 2.0; -1.7 and -2,7 gauss. In order to study the involvment of the protons in the electronic relaxation of the radicaIs, the relaxation times T1 and T2 were estimated in the temperature range -160&#176C 25&#176C for many orientations and comparing data for the protonated and deuterated radicaIs II and III, using the continuous wave saturation method. It is shown that the relaxation time T2 is practically constant in the temperature range studied and that it is sistematically greater for the deuterated radical implying narrower lines. The spin-lattice relaxation time TI is dependent upon the orientation of the magnetic field for both radicaIs. In general a linear temperature dependence of T1-1 versus T is obtained and a mechanism of tunelling of protons between close potential walls in used to explain this behavior. In the case of the protonated radical for many orientations of the magnetic field a break is observed in the T1-1 versus T curve around -60&#176C for the deuterated radical this is observed only for fewer orientations. This behaviour could be explained as due to the freezing of hydrogen bonds vibration near this temperature. For many orientations it is also observed that below -100&#176C a broadening of the ESR lines occurs which is probably re1ated to the freezing of the rotations of the methyl groups of the radical, in the case of II, and of the hast I in the case of radical III

Este documento de Tese é o resultado de um trabalho de pesquisa voltado à análise cristalográfica de novas formas sólidas cristalinas derivadas de fármacos antirretrovirais, diante do contexto da engenharia de cristais para o desenho das novas formas sólidas, e principalmente diante da ótica da análise das densidades de carga, o que permitiu um entendimento mais acurado da estrutura eletrônica molecular desta classe de compostos. Compostos farmacêuticos antirretrovirais do tipo inibidores nucleosídeos da transcriptase reversa (INTRs), são de grande importância, uma vez que são amplamente usados na terapêutica antirretroviral, principalmente contra o vírus HIV. Nesse contexto, são conhecidos alguns problemas associados na manufatura destes fármacos, principalmente aos processos de extração e purificação dos fármacos Lamivudina (3TC) e Emtricitabina (FTC). Diante desta problemática, a engenharia de cristais fornece uma solução, mediante o planejamento racional de formas sólidas (sais, cocristais, solvatos, polimorfos, etc.) que apresentam maior estabilidade e facilitem principalmente o processo de purificação em grande escala. Daí surge a importância de estudar a estrutura molecular das diferentes formas sólidas derivadas destes fármacos, sendo uma das principais técnicas para este estudo a difração de raios X em monocristais (DRXM). Neste trabalho um total de nove novas formas sólidas foram avaliadas e reportadas, com uma discussão detalhada das conformações moleculares e supramoleculares. Entretanto, é realizada uma análise das densidades de carga mediante métodos experimentais, uma vez que foram conduzidos experimentos de DRXM em alta resolução, em virtude da boa qualidade dos cristais que algumas das formas sólidas apresentaram. Desta maneira foi possível propor modelos de densidade de carga experimentais construídos mediante o formalismo de Hansen & Coppens, utilizando refinamento por mínimos quadrados baseados nos dados de difração em alta resolução. Por último, com o intuito de ter um estudo mais completo e detalhado da estrutura eletrônica, foram realizados cálculos teóricos de primeiros princípios em condições gasosas e periódicas de contorno. Desta forma, é apresentada uma sinergia entre os resultados obtidos pelas análises das distribuições de densidade de cargas de algumas formas sólidas, com os resultados gerais da engenharia de cristais e, portanto, concluir e extrapolar alguns aspectos importantes, principalmente no que se refere às energias associadas com as interações intermoleculares. A sinergia dos estudos de engenharia de cristais e de densidade de carga, é um tipo de pesquisa pouco publicada dentro da área da cristalografia de pequenas moléculas. / This Thesis is the result of the research proposal aimed to the crystallographic analysis of new crystalline solid forms derived from antiretroviral drugs, in the context of the crystal engineering for the design of the new solid forms, mainly since the viewpoint of the charge density analysis, which allowed an accurate comprehension of the molecular electronic structure of this kind of compounds. Antiretroviral drug compounds of nucleoside analog reverse-transcriptase inhibitors (NRTI) type, are of great importance once they are large used in the antiretroviral therapy, mainly against the HIV. In this context, some problems are known regard to the manufacture process of these drugs, mainly in the extraction and purification procedures of the lamivudine (3TC) and emtricitabine (FTC) drugs. On this issue, the crystal engineering provides an answer, through the rational planning of solid forms (salts, cocrystals, solvates, polymorphs, etc.) that exhibit an increased stability and facilitate mainly the large-scale purification process. Hence is important to study the molecular structure of the diverse solid forms derived from these drugs, mainly through the single-crystal X-ray diffraction (SCXD) experiments. In this research a total of nine new solid forms were assessed and reported, along with a detailed discussion of the molecular and supramolecular conformations. Meantime, it was carried out an analysis of the experimental charge density, once it was performed high-resolution SCXD experiments, since some of the solid forms showed good quality single crystals. In this way, it was possible to propose models of experimental charge density through the Hansen & Coppens formalism, using least-square refinement against high-resolution X-ray diffraction data. Finally, with the aim to have a more complete and detailed study of the electronic structure, it was also carried out first principles theoretical calculations in gas-phase and periodic boundary conditions. Thus, it is shown a synergy between the results obtained by the analysis of the charge density distributions of some solid forms and the crystal engineering results and, therefore, to conclude and to extrapolate some important aspects, mainly involved with the intermolecular interaction energies. The synergy of the crystal engineering and charge density studies is a kind of research little published, within the small molecule crystallography area.