Saline aquifers and depleted hydrocarbon fields situated beneath the North Sea are currently being proposed as storage repositories for anthropogenic CO2 captured from point source emitters in the UK and mainland Europe. Two experimental sites are already operating successfully offshore Norway: Sleipner since 1996 and Snøhvit since 2007, collectively storing several million tonnes of CO2/year in the sub-surface. Despite the apparent success of these current projects, one of the major public and scientific concerns is the ability of storage sites to retain CO2 on the millennial timescales required for CO2 plume stabilisation and dissolution. Some areas of the North Sea are also known to contain palaeo-gas seepage pathways within overburden sediments that overlie deeper hydrocarbon reservoirs (e.g. Witch Ground Graben). These areas either need to be avoided for CO2 storage or rigorously assessed in terms of leakage risk. Since the Sleipner storage site lies within such a province, this thesis delivers a detailed evaluation of the Nordland Group overburden and a critical assessment of its long-term sealing capability for CO2. From interpretation and detailed mapping of a baseline 3D seismic dataset (acquired before CO2 injection operations commenced in 1996), we have identified numerous palaeo-migration pathways and high-amplitude seismic anomalies within the Nordland Group overburden sediments deposited above the Sleipner CO2 storage site. We attributed these features to thermogenic or biogenic gas migration, accumulation and bio-degradation over geological time. We also mapped a complex network of sand-filled, glacial channels and tunnel valleys distributed within a few hundred metres below seabed and highlighted their significance as potential fluid migration networks and/or secondary storage containment for leaking CO2. Of further significance, we confirmed that these overburden features also create spatial density variations that impact on the accuracy of seismic time-depth conversions, resulting in the probability of topographic distortions being propagated into seismic interpretations and models. To the best of our knowledge no such detailed mapping of the Nordland Group overburden at Sleipner has been undertaken previously. To determine whether the top layer of the CO2 plume at Sleipner might encounter these relict pathways as it ascends and migrates laterally beneath the caprock, we evaluated the critical column heights required for a CO2 accumulation to enter such a pathway under a range of storage conditions for a CH4/CO2/brine system; assuming that these pathways currently contain methane gas. Risking scenarios were based on a range of phase saturation, pressure, temperature, density, viscosity, interfacial tension and wettability conditions likely to be encountered at depths commensurate with the caprock at Sleipner. We concluded that given certain conditions at the caprock, CO2 could leak more easily into palaeo-migration pathways than CH4 (i.e. at lower entry pressures and therefore smaller column heights), assuming that brine densities and, most importantly, pore radii have not changed significantly over geological time (i.e. no cementation or dissolution has taken place). To further understand the dynamic significance of these palaeo-migration pathways, channels and tunnel valleys, including their ability to form inter-connected leakage/migration networks, we constructed a series of high-resolution 3D models of the Sleipner storage site and overburden, then used stochastic basin modelling and simulation techniques to investigate the processes involved during the introduction of CO2 into the storage site over a prolonged time period. Models were populated with geological, stratigraphic and structural information derived from our seismic interpretation. Flow simulations were calibrated to published data and matched to the present-day plume distribution. The absence of observational reservoir pressure and temperature data from Sleipner introduces significant uncertainty to model outcomes with respect to CO2 density and column height estimates and to surmount this difficulty we constrained the caprock temperature to CO2 density estimates obtained from the most recent gravity data observations at Sleipner. We concluded that the overburden heterogeneity is significant and palaeo-migration pathways, highpermeability channels and tunnel valleys at Sleipner may become potential migration pathways for CO2 as the plume continues to spread laterally over the coming decade, but the possible storage response is difficult to quantify given the absence of sufficient overburden rock property information and accurate pressure and temperature data for the storage site. The overall conclusion from this work is that insufficient information was collected within the Sleipner area prior to storage site development and too many significant studies which should have been performed as a pre-requisite (e.g. obtaining a caprock sample for laboratory testing of potential seal capacity), were actually performed some years after CO2 injection operations had already commenced. The pressure and temperature conditions at the caprock depth for the Sleipner storage site are also marginal in terms of maintaining CO2 above critical point conditions in dense phase and thus maximising storage efficiency. Most significantly, no rigorous overburden mapping and risking was performed for Sleipner (such as the work described in this thesis), thus the fact that no leakage has been detected at Sleipner is more due to good fortune than following best practices. Hopefully, our work has highlighted these key deficiencies so that future CO2 storage site feasibility and development studies will be performed more diligently.

We propose a hypothesis and a numerical model for the formation of branching plagioclase textures visible at both macroscopic (∼cm to ∼m) and microscopic scale within melagabbro of the Isle of Rum, Scotland, based on macroscopic, microscopic observations and relevant geological history. The plagioclase crystals are typically linked as twins and form meshes of planar stellate structures (m-scale) with a large range in geometrical organization from patchy to radiating. Evidence of macroscopic crystal aggregation and alignment is attributed to interfacial free energy minimization at the microscopic scale during growth. Accordingly, a binary immiscible Lattice Boltzmann model was developed to simulate diffusion of simplified plagioclase in the melt phase. Isothermal phase transitions modelled via first order chemical reactions are subsequently coupled with stochastic dynamics at the crystal growth front to simulate energy minimization processes including twinning during crystallization in an igneous environment. The solid phase and the liquid phase are coupled with a temporal flexibility that sets the overall ratio between the rate of diffusion and chemical enrichment in the liquid state and the rate of crystallization. The parameter space of the model is explored extensively, followed by a reasonable transcription of physical parameters and an estimation of other parameters to construct realistic simulation scenarios yielding synthetic plagioclase stellates. The results are presented, analyzed and discussed. They appear to be in reasonable qualitative agreement with observations, and several aspects of the natural stellates such as the stellate spacing and long continuous stretches of plagioclase with epitaxial junctions seem to be in reasonable quantitative agreement with observations.

The thesis entitled “Addressing subtle physicochemical features exhibited by molecular crystals via Experimental and Theoretical Charge Density Analysis” consists of five chapters. An introductory note provides a brief description of experimental and theoretical charge density methodology, followed by its utilization in obtaining certain physical and chemical properties in molecular crystals. Chapter 1 addresses not so easily accessed molecular property arising due to electron conjugation, highlighting antiaromaticity in tetracyclones. A systematic study of six tetracyclone derivatives with electron withdrawing and electron donating substituents has been carried out using experimental and theoretical charge density analysis. A three pronged approach based on quantum theory of atoms in molecules (QTAIM), nucleus independent chemical shifts (NICS), and source function (SF) has been employed to establish the degree of antiaromaticity of the central five-membered ring in all the derivatives. Electrostatic potentials mapped on the is density surface reveal the finer effects of different electron withdrawing and electron donating substituents on the carbonyl group. Chapter 2 presents a temperature induced reversible first order single crystal to single crystal phase transition (Room temperature Orthorhombic, P22121 to low temperature Monoclinic, P21) in a  hybrid peptide, Boc-γ4(R)Val-Val-OH. The thermal behavior accompanying the phase transition of the dipeptide crystal was characterized by differential scanning calorimetry, visual changes in birefringence of the sample during heating and cooling cycles on a hot-stage microscope with polarized light. Variable-temperature unit cell check measurements from 300 to 100 K showed discontinuity in the volume and cell parameters near the transition temperature, supporting the first-order behavior. The reversible nature of the phase transition is traced to be due to an interplay between enthalpy and entropy. Chapter 3 brings out an unusual stabilizing interaction involving a cooperative -hole and ¬hole character in a short NCS···NCS bond. This chapter describes structural features of four isothiocyanate derivatives, FmocXCH2NCS; X=Leu, Ile, Val and Ala. Among these it is observed that only FmocLeuCH2NCS which crystallizes in a tetragonal space group, P41, (a=b=12.4405(5) Å; c= 13.4141(8) Å) transforms isomorphously to a low temperature form, P41, (a=b=17.4665(1) Å; c= 13.1291(1) Å). The characteristics of the phase transition have been monitored by Differential Scanning Calorimetry, variable temperature IR and temperature dependent unit cell measurements. The short NCS···NCS intermolecular interaction (3.296(1) Å) is analyzed based on detailed experimental charge density analysis which reveals the nature of this stabilizing interaction. Chapter 4 explains a comparative study of syn and anti conformations of carboxylic acids in peptides from both structural aspect and charge density features. Single crystal structures of four peptides having syn conformations [BocLeuγ4(R)Valγ4(R)ValOH, BocLeuγ4(R)ValLeuγ4(R)ValOH, Boc3(S)Leu3(S)LeuOH] and one with anti conformation, BocLeuγ4(R)ValValOH have been analyzed. Experimental charge density analysis has been carried out exclusively on BocLeuγ4(R)ValValOH having anti form, because of its rare occurrence in literature. However, low temperature datasets on the four peptides with syn conformations were collected and theoretical charge density analysis has been carried out on two of these compounds. Electrostatic potentials mapped on is density surface bring out a significant difference at the oxygen atoms of the carboxyl group in the two conformations. However, lone pair orientation of different types of Oxygen atoms in the two forms (urethane, amide, acid) doesn’t exclusively indicate the differences in the corresponding charge density features. Chapter 5 addresses the issue of how sensitive are the charge density features associated with amino acid residues when the backbone conformational angles are varied. Three model systems, 1, L-alanyl–L-alanyl–L-alanine dehydrate; 2, anhydrous L-alanyl–L-alanyl–L¬alanine and 3, cyclo-(D,L-Pro)2(L-Ala)4 monohydrate have been chosen for this evaluation. Compound 1 has ant parallel alignment of tripe tide strands, and compound 2 has parallel alignment. All the alanine residues in compound 1 and 2 are in the -sheet region of the Ramachandran plot, whereas, the four Alanine residues in the cyclic hex peptide 3 span different regions of the Ramachandran plot. Theoretical multipole modelling has been carried out in order to explore the plausibility of transferring multipole parameters across different regions of Ramachandran Plot. Appendix I contains a brief description of charge shift bonding in Ph-CH2-Se-Se-CH2-Ph, as determined based on both experimental and theoretical charge density analysis. Appendix II contains a reprint of a published article on “Conformation-Changing Aggregation in Hydroxyacetone: A Combined Low-Temperature FTIR, Jet, and Crystallographic Study”.

No description available.

Ce manuscrit est consacré à l'étude des transformations polymorphiques induites au cours du procédé de compression directe, et à son incidence sur les propriétés mécaniques des comprimés. L'objectif principal de ce travail est d'apporter des éléments de compréhension sur la transition polymorphique de la caféine (principe actif modèle) Forme I en Forme II survenant lors du procédé de compression directe, et de déterminer si celle-ci a un impact sur la contrainte à la rupture du comprimé. L'utilisation du simulateur de compression Styl'One Classique (Médel'Pharm) et d'une machine de fatigue (Instron®) pour la fabrication des comprimés, a permis d'étudier deux paramètres de procédé (pression et vitesse de fabrication) et deux paramètres de formulation (dilution du principe actif et nature du diluant) représentatifs de conditions industrielles. Les transitions de phase de la caféine ont été évaluées par analyse calorimétrique différentielle (ACD). De plus, des études cinétiques ont été conduites durant plusieurs mois afin d'observer l'influence de ces différents paramètres sur la transition polymorphique de la caféine anhydre Forme I en Forme II dans les comprimés au cours de leur stockage. Enfin, l'analyse du mécanisme de transition de ce principe actif a été réalisée au moyen d'une loi exponentielle étirée, issue du modèle de Johnson-Mehl-AvramiLa contrainte à la rupture des comprimés (caractéristique globale) a été mesurée par un test de rupture diamétrale, la dureté de surface des comprimés (caractéristique locale) par nano-indentation. Un premier modèle de prédiction de la contrainte à la rupture selon la teneur en caféine a été développé. Les principales caractéristiques du cycle de compression calculées à partir des données enregistrée par le simulateur de compression ont permis d'analyser le comportement des formules lors de la compression puis d'établir un second modèle de prédiction de la contrainte à la rupture.Les résultats de transition polymorphique et de propriétés physiques de comprimés seront alors confrontés / Direct compression process is widely used in the pharmaceutical industry for tablet manufacturing. This work is dedicated to the study of the polymorphic transformation induced by a direct compression process, and its impact on tablet mechanical properties. The main objective is to improve the understanding of the phase transition of caffeine Form I into Form II occurring during the direct compression process, and whether it has an impact on the tablet tensile strength. In this way, several studies have been conducted on the impact of operating conditions on the polymorphic transformation of a model active pharmaceutical ingredient (API) and on few physical properties of the tablets.The use of a compression simulator Styl’One Classique (Médel’Pharm) and a fatigue equipment (Instron®) for the manufacture of tablets, allowed studying two process parameters (compression load and compression speed) and two formulation parameters (dilution of the API and nature of the diluent). Caffeine phase transitions have been evaluated by differential scanning calorimetry (DSC). Moreover, during several months after tableting, kinetic studies were conducted in order to observe the influence of these parameters on the polymorphic transition of the anhydrous caffeine Form I into Form II in tablets during storage. Finally, the analysis of the transition mechanism of this API was performed thanks to a stretched exponential law, derived from the Johnson-Melh-Avrami model.The tensile strength of tablets (global property) was measured by a diametral compression test and their surface hardness (local property) by nanoindentation. A first predictive model for tablet tensile strength according to the caffeine content was developed. The compression cycle characteristics calculated from the data recording with the compression simulator allowed analyzing the behavior of different blends during the compression process. A second model for predicting the tensile strength was then established.Finally, results obtained for the polymorphic transition and physical properties of tablets will then be confronting

LIMA JÚNIOR, José Alves de. Espectroscopia Raman dos Aminoácidos L - metionina e DL - alanina e de Nanotubos de Carbono. 2008. 214 f. Tese (Doutorado) - Programa de Pós-Graduação em Física, Centro de Ciências, Departamento de Física, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-05-13T22:56:00Z No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-05-14T18:26:53Z (GMT) No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) / Made available in DSpace on 2014-05-14T18:26:53Z (GMT). No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) Previous issue date: 2008 / This work describes polarized Raman scattering measurements in L-methionine and in DL-alanine (two amino acids) crystals and in several samples of single-walled carbon nanotubes (SWNT). In L-methionine crystal the Raman spectra were obtained from 17 K to 295 K in the spectral range from 50 cm-1 to 3100 cm-1, but no indication of a phase transition was observed. At room temperature, Raman scattering measurements were also performed for pressure up to 5 GPa. Several changes observed in the spectra were interpreted as due to structural phase transition undergone by L-methionine crystal at ~ 2.1 GPa. The results for decompression show that the phase transition is reversible with a hysteresis of ~ 0.8 GPa. In DL-alanine crystal the Raman spectra were obtained at temperatures from 15 K to 295 K over the spectral range 50 cm-1 - 3100 cm-1. No evidence of structural phase transition was found in this range of temperature, although information about diverse modes of the crystal were furnished. Samples of SWNT’s studied were prepared with metallic catalysts using the arc voltaic method. MnNiCo was the main compound of the first series and FeNiCo, the main compound of the second. In both sets it was observed that Cerium (Ce) insertion induces in the sub-set, probed with the 2.41 eV excitation energy, a narrowing of the diameter distribution favoring the tubes with smaller diameter. The Raman scattering measurements in a commercial sample of SWNT’s show a discontinuity at about 2 GPa. The discontinuity was represented by a changing in the slope of the frequency versus pressure for tangential modes. The measurement was performed twice, using two different solutions of surfactants, sodium dodecil sulfate (SDS) and plurocic acid F127 (F127), and the results were similar. The anomaly was interpreted as due to the deformation of the tubes as predicted theoretically. Two sets of three samples of SWNT’s containing different levels of lithium insertion were also analyzed by Raman spectroscopy. Each set of sample was formed by a sample with lithium, a sample without lithium and a sample with partial insertion of lithium. The results show that the lithium is efficiently intercalated with both lithium containing compound (LiCO3/NiO/CoO and LiNi0.5Co0.5O2), but the mechanism of intercalation differs from one to the other. The intercalation is unstable when lithium is intercalated interstitially (LiNi0.5Co0.5O2) and it can be removed almost completely by washing the sample, but if the lithium is intercalated inside the tubes (LiCO3/NiO/CoO) it can not be removed by the same process. / No presente trabalho foram realizadas medidas de espalhamento Raman polarizado em cristais de L-metionina e de DL-alanina (dois aminoácidos) e em diversas amostras de nanotubos de carbono de parede simples (SWNT). As medidas de espalhamento Raman em cristais de L-metionina foram realizadas no intervalo espectral entre 50 cm-1 e 3100 cm-1 desde a temperatura ambiente até a temperatura de 17 K. No intervalo de temperatura estudado a estrutura da L-metionina manteve-se estável. À temperatura ambiente também foram realizadas medidas Raman em altas pressões hidrostáticas. A máxima pressão atingida foi de 4,7 GPa e diversas modificações nos modos associados às unidades CO2, NH3, CC, CS, CH, CH2 e CH3 sugerem que a L-metionina sofre um transição estrutural de fase em torno de 2,1 GPa com histerese de aproximadamente 0,8 GPa. No cristal de DL-alanina foram realizadas medidas de espalhamento Raman no intervalo de temperatura de 15 K a 295 K. Embora nenhuma mudança significativa tenha sido observada neste intervalo de temperatura, os resultados são importantes para se entender o comportamento de uma molécula fundamental na constituição das proteínas. Medidas de espalhamento Raman em SWNT’s foram realizadas em amostras preparadas pela técnica de arco voltáico, utilizando-se vários catalisadores metálicos. As amostras foram divididas em duas séries: A primeira com os catalisadores à base de MnNiCo e a segunda à base de FeNiCo. Em ambas as séries observou-se que a inserção de Cério (Ce) foi responsável por tornar a distribuição de diâmetros do subconjunto ressonante com a energia 2,41 eV mais estreita. Além disso, o máximo da distribuição é deslocado para o azul, provavelmente em conseqüência da seleção de tubos de menor diâmetro dentro do subconjunto estudado. A inserção de Zircônio (Zr) à segunda série não trouxe mudanças significativas. Foram realizadas medidas de espalhamento Raman em função da pressão hidrostática em uma amostra comercial de SWNT. Como fluido transmissor foram utilizadas soluções de dois surfactantes: o dodecil sulfato de sódio (SDS) e o ácido plurônico F127 (F127). Devido à baixa relação sinal-ruído, não foi possível estudar o comportamento dos modos de respiração radial (RBM), mas pela descontinuidade do gráfico da freqüência em função da pressão dos modos tangenciais em aproximadamente 2 GPa é provável que os nanotubos sofram uma transição de fase estrutural nessa pressão, com deformação da seção circular dos tubos como predito por estudos teóricos. Dois conjuntos de amostras contendo diferentes níveis de inserção de lítio também foram estudados por espectroscopia Raman. Cada conjunto era formado por uma amostra sem lítio, uma com lítio e a terceira com inserção parcial de lítio (obtida pela lavagem da amostra que contém lítio). Nos dois conjuntos a inserção foi eficiente, contudo o mecanismo de inserção é diferente de uma série para outra. Na primeira série o catalisador utilizado para a inserção de lítio foi LiNi0,5Co0,5O2. Com este composto o lítio é intercalado intersticialmente e pode ser removido quase que completamente pela lavagem da amostra. Já na segunda série o composto utilizado foi LiCO3/NiO/CoO o que fez com que o lítio fosse intercalado dentro dos tubos de modo a não ser removido pela lavagem da amostra.

SILVA, José Gláucio da. Propriedades Vibracionais do Dipeptídeo L-Alanil-Alanina submetido a deformações homogêneas. 2015. 131 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2016-03-18T16:45:00Z No. of bitstreams: 1 2015_tese_jgsilva.pdf: 4602304 bytes, checksum: c589f914ff64a0ac8fd63892133504ba (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2016-03-18T16:46:19Z (GMT) No. of bitstreams: 1 2015_tese_jgsilva.pdf: 4602304 bytes, checksum: c589f914ff64a0ac8fd63892133504ba (MD5) / Made available in DSpace on 2016-03-18T16:46:19Z (GMT). No. of bitstreams: 1 2015_tese_jgsilva.pdf: 4602304 bytes, checksum: c589f914ff64a0ac8fd63892133504ba (MD5) Previous issue date: 2015 / The dipeptide L-Alanyl – L-Alanine crystal was studied through polarized Raman scattering submitted to homogeneous deformations. The crystals were grown by slow evaporation technique from an aqueous supersaturated solution of the crystal powder. Rays-x diffractions measurements were realized to confirm a crystalline structure of the crystal. Polarized Raman scattering measurements were performed at room temperature, as well as the analysis of the group theory to the C4 factor group and a tentative assignment of the vibrational modes of crystal. Raman scattering measurements in the crystals as a function of temperature were realized between two intervals of temperature: first, at low temperature between 300 K and 11 K e 11 K and 300 K, and second, at high temperature between 300 K e 520 K and 520 K e 300 K, in the spectral range of 50 cm-1 to 3400 cm-1. From the results of low temperature measurements, it was possible to conclude that the crystal undergoes a second-order phase transition between 80 K and 60 K, from a tetragonal structure with C4 factor group to a monoclinic structure with C2 factor group, maintaining the same number of the molecules per primitive cell. The suggested mechanism to explain the phase transition is the occupation of non-equivalent sites by CH3 molecular groups present at Ala-Ala molecule. On the other hand, the crystal remained stable in the high temperature range studied, and the changes observed in the Raman spectra showed no evidence that the Ala-Ala crystal undergone phase transition or changes in molecule conformation. In those experiments were observed only quantitative changes in frequency and widths of the Raman modes, which are normal for any material subjected to variations in temperatures around 220 K. Raman scattering measurements in the crystals as a function of pressure in the pressure range between 0,1 GPa and 6,3 GPa, in compression and of 6,3 GPa and 0,1 GPa, in decompression, in the spectral region between 100 cm-1 and 3400 cm-1 showed two ranges where several qualitative changes occurred; the first, in low pressure interval between 1.7 GPa and 2.3 GPa and the second, at high pressure interval, between 4.5 GPa and 4.9 GPa. Between 1.7 GPa and 2.3 GPa, it was observed qualitative changes as well as the disappearance of an external mode around of 130 cm-1 and the anomalous behavior of other external mode around of 110 cm-1 for pressures of the order of 1,7 GPa. These qualitative changes suggest that the crystal exhibits a second order structural phase transition. Qualitative changes also were observed in others regions of the Raman spectrum through of special reorientation of the molecular groups CO2, CH3 and NH3. These qualitative changes characterize a structural second order phase transition. The mains qualitative changes observed between 4,5 GPa and 5,2 GPa were the disappearance of the external modes and the an large increasing of the width of the Raman modes, suggesting that the crystal exhibits a structural disorder in the crystalline structure when undergoes a phase transition for high pressures, possibly a amorphization. When performing decompression of the sample, the Raman spectrum returns to its initial form relative to pressure of 0,1 GPa indicating reversibility of phase transitions. / O cristal dipeptídeo L-Alanil-L-alanina (Ala-Ala) foi estudado através da técnica de espalhamento Raman polarizado submetido a deformações homogêneas. Os cristais foram crescidos pela técnica de evaporação lenta a partir de uma solução aquosa supersaturada do pó do cristal. Medidas de raios-x foram realizadas para confirmar a estrutura cristalina do cristal. Foram realizadas medidas de espalhamento Raman polarizado a temperatura ambiente, bem como análise da teoria de grupos para o grupo fator C4 juntamente com uma classificação exploratória dos modos normais de vibração do cristal. As medidas de espalhamento Raman foram realizadas em baixas temperaturas, entre 300 K e 11 K e 11 K e 300 K, e altas temperaturas, entre 300 K e 520 K e 520 K e 300 K, na região espectral de 50 a 3300 cm-1. Da análise dos resultados das medidas de baixas temperaturas foi possível concluir que o cristal exibe uma transição de fase de segunda ordem, entre 80 e 60 K, passando continuamente da estrutura tetragonal com grupo fator C4 para uma estrutura monoclínica com grupo fator C2 mantendo o mesmo número de moléculas na célula primitiva. O mecanismo proposto para explicar a transição de fase é a ocupação de sítios de simetria C1 não equivalentes pelos íons moleculares CH3 numa estrutura monoclínica pertencente ao grupo fator C2. O cristal manteve-se estável em todo o intervalo de alta temperatura estudado. Nestas experiências foram observadas apenas mudanças quantitativas nas frequências e larguras de linha dos modos Raman estudados, que é normal para qualquer material submetido a variações de temperaturas da ordem de 220 K. Medidas de espalhamento polarizado no cristal de Ala – Ala no intervalo de pressão entre 0,1 GPa e 6,3 GPa, na compressão, e de 6,3 GPa e 0,1 GPa, na descompressão, na região espectral de 100 cm-1 a 3400 cm-1 mostraram dois intervalos de pressão em que ocorrem diversas mudanças qualitativas; o primeiro entre 1,7 GPa e 2,3 GPa e o segundo entre 4,5 GPa e 4,9 GPa. Entre 1,7 GPa e 2,3 GPa foram observadas mudanças qualitativas significantes na região dos modos externos, tais como, o desaparecimento de um modo da rede em torno de 130 cm-1 e o comportamento anômalo de outro modo da rede em torno de 110 cm-1 para pressão de 1,7 GPa. Estas mudanças qualitativas sugerem que o cristal exibe uma transição de fase estrutural de segunda ordem. As outras regiões do espectro Raman do cristal apresentaram diversas mudanças qualitativas continuas no comportamento dos modos Raman das unidades que participam diretamente das pontes de hidrogênio, indicando que o cristal apresenta reorientações espaciais dos grupos moleculares CO2, CH3 e NH3. Estas mudanças qualitativas caracterizam uma transição de fase estrutural de segunda ordem. As principais mudanças qualitativas observadas entre 4,5 GPa e 5,2 GPa são o desaparecimento dos modos externos e, quantitativamente, um grande aumento na largura de linha dos modos Raman indicando que o cristal exibe uma desordem na estrutura cristalina durante a transição de fase de altas pressões, possivelmente uma amorfização. Na descompressão da amostra os espectros Raman são quase que totalmente recuperados na sua forma inicial indicando que o cristal apresenta transições de fase reversíveis.

Piezoelectric materials find use as actuators and sensors in automotive, aerospace and other related industries. Automotive applications such as fuel injection nozzles and engine health monitoring systems require operating temperatures as high as 300-500 oC. The commercially used piezoelectric material PbZr1-xTixO3 (PZT) is limited to operating temperatures as low as 200 oC due to the temperature induced depolarization effects. PZT, in the undoped state exhibits a piezoelectric coefficient (d33) of 223 pC/N and ferroelectric-paraelectric transition temperature (Tc) of 386 oC. The enhanced properties of PZT occur at a region between the tetragonal and rhombohedral phases, called the Morphotropic Phase Boundary (MPB). Therefore, search for new materials with higher thermal stability and better sensing capabilities were focused on systems that exhibit a PZT-like MPB. This led to the discovery of (x)BiScO3-(1-x)PbTiO3 (BSPT), which exhibits an MPB with enhanced Tc (450 oC) and exceptionally high piezoelectric response (d33 = 460 pC/N). Theoretical studies have shown that the mechanism of enhanced piezoresponse in ferroelectric systems is related to the anisotropic flattening of the free energy profiles. An alternative view point attributes the anomalous piezoelectric response to the presence of high density of low energy domain walls near an inter-ferroelectric transition. Diffraction is a versatile tool to study the structural and microstructural changes of ferroelectric systems upon application of electric field. However, characterization of electric field induced structural and microstructural changes is not a trivial task, since in situ electric field dependent diffraction studies almost invariably give diffraction patterns laden with strong preferred orientation effects, due to the tendency of the ferroelectric/ferroelastic domains to align along the field direction. Additionally, diffraction profiles of MPB compositions exhibit severe overlap of Bragg peaks of the coexisting phases, and hence, it is difficult to ascertain with certainty, if the alteration in the intensity profiles upon application of electric field is due to change in phase fraction of the coexisting phases or due to preferred orientation induced in the different phases by the electric field. The characterization of electric field induced phase transformation in MPB systems, has therefore eluded researchers and has been considered of secondary importance, presumably due to the difficulties in unambiguously establishing the structural changes upon application of electric field. In fact, majority of the in situ electric field dependent diffraction studies have been carried out on compositions just outside the MPB range, i.e. on single phase compositions. In such studies, the focus has been mainly on explaining the piezoelectric response in terms of motions of the non-180° domain walls and field induced lattice strains. In this dissertation, the BSPT system has been systematically investigated with the view to understand the role of different contributing factors to the anomalous piezoelectric response of compositions close to the MPB. Using a comparative in situ electric field dependent diffraction study on a core MPB composition exhibiting highest piezoelectric response and a single phase monoclinic (pseudo-rhombohedral) composition just outside the MPB, it is demonstrated that, inspite of the significantly large domain switching and lattice strain (obtained from peak shifts) in the single phase composition, as compared to the MPB composition, the single phase composition shows considerably low piezoelectric response. This result clearly revealed that the anomalous piezoelectric response of the MPB composition is primarily associated with field induced inter-ferroelectric transformation and the corresponding field induced interphase boundary motion. A simple strategy has been employed to establish the field induced structural transformation for the MPB compositions, by overcoming the experimental limitation of in situ electric field dependent diffraction studies. The idea stemmed from the fact that, if the specimens for diffraction study can be used in powder form instead of pellet, the problems associated with preferred orientation effects can be eliminated, and the nature of field induced structural changes can be accurately determined. A comparative study of the diffraction profiles from poled (after subjecting the specimen to electric field) and unpoled (before subjecting the specimen to electric field) powders could precisely establish the nature of electric field induced phase transformation for the MPB compositions of BSPT and provided a direct correlation between the electric field induced structural changes and the enhanced piezoelectric response. A new ‘powder poling’ technique was devised, which involves application of electric field to powder form of the specimen. Using this technique, it was possible to study separately, the effect of stress and electric field on the nature of structural transformation. A unique outcome of this study was, it could demonstrate for the first time, analogous nature of the stress and electric field induced structural transformation. A comparative study of the dielectric response of poled and unpoled samples was used to show a counterintuitive phenomenon of field induced decrease in polarization coherence for the MPB compositions. This approach was used to suggest that the criticality associated with the MPB extends beyond the composition boundary conventionally reported in literature based on bulk diffraction techniques (x-ray and neutron powder diffraction). The layout of the dissertation is as follows: Chapter 1 gives a brief introduction of the fundamental concepts related to ferroelectric materials. The theories that explain the enhanced piezoresponse of MPB based ferroelectric systems have been outlined. Detailed information of the existing literature is presented in the relevant chapters. Chapter 2 presents the details of the solid state synthesis of BSPT compositions and structural analysis using diffraction studies. The dielectric measurements were used to establish the Tc for the different compositions. The enhanced ferroelectric and piezoelectric properties were observed for the MPB compositions, which were shown to exhibit coexistence of tetragonal and monoclinic phases from structural studies. The critical MPB composition exhibiting highest piezoelectric and ferroelectric properties was established to be x = 0.3725. The thermal stability of the critical MPB composition was established to be 400 oC using ex situ thermal depolarization studies. The common approach of structural analysis in the unpoled state failed to provide a unique relationship between the anomalous piezoelectric response and the structural factors at the MPB, emphasizing the need to characterize these system using electric field dependent structural studies. Chapter 3 presents the results of in situ electric field dependent diffraction measurements carried out at Argonne National Laboratory, USA. The quasi-static field measurements could successfully quantify the non-180o domain switching fractions and the field induced lattice strains. The changes in the integrated intensities were used to obtain the non-180o domain switching fraction and the shift in peak positions were used to quantify the field induced lattice strains. The in situ studies could successfully explain the macroscopic strain response for the single phase pseudo-rhombohedral (monoclinic) composition on the basis of domain switching mechanisms and field induced lattice strains. The MPB compositions were shown to have additional contributions from interphase boundary motion, resulting from change in phase fraction of the coexisting phases. The results emphasized the need to investigate the electric field induced transformation for MPB compositions, in order to give a comprehensive picture of the various contributions to the macroscopic piezoreponse. While Rietveld analysis could be used to investigate the phase transformation behaviour upon application of electric field, textured diffraction profiles obtained using in situ studies, in addition to the severely overlapping Bragg reflections of the coexisting phases for the MPB compositions hindered reliable estimation of the structural parameters. An alternate approach to investigate the field induced phase transformation is presented in Chapter 4. The stroboscopic measurements on the MPB composition showed evidence of non-180o domain wall motion even at sub-coercive field amplitudes as low as 0.1 kV/mm. Chapter 4 presents the results of the ex situ electric field dependent structural study, wherein the diffraction profiles collected from poled powders is compared to that of unpoled powders. The diffraction profiles from the poled powders did not exhibit any field induced crystallographic texture and could successfully be analyzed using Rietveld analysis. High resolution synchrotron diffraction studies (ESRF, France) carried out on closely spaced compositions revealed that, the composition exhibiting the highest piezoelectric response is the one, which exhibits significantly enhanced lattice polarizability of both the coexisting (monoclinic and tetragonal) phases. The enhanced lattice polarizability manifests as significant fraction of the monoclinic phase transforming irreversibly to the tetragonal phase after electric poling. The monoclinic to tetragonal transformation suggested the existence of a low energy polarization rotation pathway towards the [001]pc direction in the (1 1 0)pc pseudocubic plane of the monoclinic phase. The results are discussed on the basis of the existing theories that explain piezoresponse in MPB systems and are in support of the Polarization rotation model, in favor of a genuine monoclinic phase. Chapter 5 discusses the ferroelectric-ferroelectric stability of the MPB compositions in response to externally applied stress and electric field independently. Using the newly developed ‘powder poling’ technique, which is based on the concept of exploiting the irreversible structural changes that occur after application of electric field and stress independently, it was possible to ascertain that, both moderate stress and electric field induce identical structural transformation - a fraction of the monoclinic phase transforms irreversibly to the tetragonal phase. The powder poling technique was also used to demonstrate field induced inter-ferroelectric transformation at sub-coercive field amplitudes. In addition, the analysis of the dielectric response before and after poling revealed a counterintuitive phenomenon of poling induced decrease in the spatial coherence of polarization for compositions around the MPB and not so for compositions far away from the MPB range. Exploiting the greater sensitivity of this technique, it was demonstrated that, the criticality associated with the inter-ferroelectric transition spans a wider composition range than what is conventionally reported in the literature based on bulk x-ray/neutron powder diffraction techniques. Chapter 6 presents the closure and important conclusions from the present work and summarizes the key results, highlighting the proposed mechanism of enhanced piezoresponse in BSPT. The last part of the chapter deals with suggestions for future work from the ideas evolved in the present study. vi

Les comportements thermiques d'une suspension granulaire en deux dimensions maintenue dans un état stationnaire hors équilibre ont été étudiés expérimentalement. L'analyse de la distribution spatiale des particules a montré qu’il existe une équation d’état reliant la densité de particules et deux autres quantités mesurables que nous interprétons comme une température et une pression granulaire. Cette équation d’état révèle l’existence d’interactions interactions attractives entre les particules. De plus, la dépendance de cette température aux différentes quantités physiques du problème montre qu'il existe deux régimes de fluctuations, que nous interprétons comme des régimes inertiels et visqueux. Dans ce dernier régime, la suspension se comporte de manière additive : il n'existe pas de corrélations à longue portée sur les fluctuations de densité, ce qui est étonnant dans une suspension où les corrélations de vitesses sont connues pour être à longue portée. Deuxièmement, le système exhibe une transition de phase ordre/désordre caractérisée par de grandes fluctuations et des hétérogénéités qui émergent proche du point critique. Ces hétérogénéités sont constituées d'amas de particules localement cristallisées dans une phase fluide désordonnée. L'analyse de la morphologie de ces structures révèlent une invariance d'échelle et a permis d'extraire plusieurs exposants critiques à l'aide d'outils de la théorie de la percolation. Troisièmement, la puissance injectée pour maintenir le système dans un état stationnaire hors équilibre peut être relié simplement à certaines quantités physiques de la suspension, et montre que l'injection de l'énergie se fait de la même manière quelque soit la phase ou le régime de fluctuations de la suspension. / The thermal-like behavior of a two-dimensional granular suspension maintained in an out-of equilibrium steady state is experimentally studied. We uncovered a state equation relating the density of particles and two measureable quantities that we interpret as a pressure and a temperature. The comparison of the equation of state to the hard disks one shows that there is attractive interaction between particles. The dependency of the temperature to the physical quantities of our suspension shows two regimes of fluctuations that we interpret as a viscous and an inertial regime. In the viscous regime, the system is additive: there is no long range correlation on fluctuations of density, which is surprising in a suspension where velocity correlations are usually known to be long ranged. Second, the system is subjected to liquid-to-crystal phase transition characterized by large fluctuations and heterogeneities that rise near the critical point. Heterogeneities are made of many locally crystallized patches of particles surrounded by a disordered fluid phase. The analysis of their morphologies shows scale invariance and allowed to extract several critical exponents using tools of percolation theory. Third, the energy flux which goes through the suspension in order to keep the system in a out of equilibrium steady state can be expressed simply with respect to physical quantities of the system, and shows that the way we inject energy is independent from the phase or the fluctuations regime of the system.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-18T11:29:37Z No. of bitstreams: 1 arquivototal.pdf: 1956067 bytes, checksum: 845c3d0cd5113c8498d955af9cdcd907 (MD5) / Made available in DSpace on 2017-09-18T11:29:37Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1956067 bytes, checksum: 845c3d0cd5113c8498d955af9cdcd907 (MD5) Previous issue date: 2016-09-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis, we deal with a particular geometric scalar tensor theory, which is a version of the Brans-Dicke gravitation, formulated in aWeyl integrable space-time. This formulation is done using the Palatini's variation procedure. The main point of our work is to perform two particular applications of the geometrical Brans-Dicke theory. The rst one is the study of geometric fase transition phenomena, that's related to a continuous change in the space-time structure of the universe from a Riemann's geometry to a Weyl's geometry, or in the inverse sense, from Weyl's geometry to Riemann's geometry. This phenomena seems to take place when the universe starts to expand in a accelerated rate. The second one is the investigation of classical and quantum behaviour of a anisotropic n-dimensional universe . To nd solutions that display the dynamical compacti cation of non observed extra dimensions is the main motivation to study such universe. / Nesta tese, reapresentamos uma teoria escalar tensorial geométrica, que é uma versão da gravitação de Brans-Dicke formulada em um espaço-tempo de Weyl integrável. Com esta teoria fazemos duas aplicações especí cas. Uma delas para o estudo de um fenômeno, que chamamos de transição de fase geométrica, uma mudança contínua na estrutura geom étrica do espaço-tempo. Este fenômeno parece ocorrer quando o universo se expande aceleradamente. A segunda aplicação reside no estudo clássico e quântico do comportamento de um modelo de universo n-dimensional anisotrópico. A motivação para esta investigação é a busca de soluções que exibem o compactação dinâmica das dimensões extras, que não são observadas.