The main material studied in this project is silicon oxide phosphate, often referred to in the literature as Si₅O(PO₄)₆. This material has highly unusual coordination of the silicon (octahedral, as well as the more common tetrahedral). The structure is hexagonal, it has been assigned to space group R -3 and lattice parameters a ≈ 7.85 Å, c ≈ 24.14 Å. This work's main focus is on understanding the interplay between structure and properties in order to enhance protonic conductivity for a fuel cell electrolyte. Silicon oxide phosphate was synthesised with the solid-state method, using a gel precursor made from H₃PO₄, water and SiO₂. Various compositions were made with different P/Si starting ratios, ranging between 0.57 - 1.5. There were small but significant differences in the a,b axes for the different compositions that corresponded to conductivity behaviour of hydrothermally treated P-Si compositions. This correlation was also found to appear in ³¹P NMR for the chemical shift at - 44 ppm for untreated P-Si compositions as well as in the temperatures of the DTA peaks for the hydrothermally treated compositions. This all implies that this particular P-Si system with the addition of water becomes a ternary system that enables protonic conductivity. A proposed mechanism for the protonic conductivity is given where it is suggested that protons flow along the internal channels of the structure using two waters that provide dual pathways for protons. This is possible through utilization of a proton thought to be in the structure (a P_OH bond of 1.57 Å). Protonic conductivity could further be increased in the system by incorporating 85% H₃PO₄ in the P-Si materials, thus these materials act as matrices for the phosphoric acid. Another composition, Ge₅O(PO₄)₆ with 5% extra germanium, was hydrothermally treated and found to have protonic conductivity at higher temperatures than the silicon oxide phosphate analogues.

No description available.

In this thesis the properties of graphene and its few-layers are engineered to make them highly conductive. Two different approaches were implemented to achieve this goal. One approach was to increase the concentration of charge carriers by intercalation of acceptor FeCl3 molecules between graphene planes. This resulted in a highly conductive yet transparent material which can be useful for applications. Another approach was to increase the mobility of carriers by means of removing surface contamination in the current annealing process. Optimal annealing parameters were found and a reproducible cleaning method was suggested.

La semi-perméation à haute température dans les matériaux conducteurs mixtes introduit des sollicitations chimiques. Ces matériaux sont donc sujets à des déformations d’origine thermique et d’origine chimique qui entraînent des contraintes thermo-chimio-mécaniques dont il convient de tenir compte pour anticiper leur tenue mécanique en service. Ce travail de modélisation en science pour l’ingénieur, intrinsèquement multiphysique, a pour but d’ouvrir la voie au calcul de structures de dimensions industrielles en adoptant une modélisation fonction des paramètres directement mesurables. Il s’articule principalement autour du développement d’un modèle macroscopique de déformation chimique. La modélisation proposée tient compte du transport de l’oxygène en transitoire. Les cinétiques d’échanges de matière à la surface du matériau avec leur conséquence en termes de chocs chimio-mécaniques sont évaluées. Pour simuler le comportement de structures complexes en trois dimensions, en régimes stationnaire et transitoire, les modèles ont été implémentés dans le code de calcul par éléments finis Abaqus. L’application porte sur un réacteur catalytique membranaire pour l’oxydation partielle du méthane en gaz de synthèse. L’histoire des sollicitations thermiques, chimiques et mécaniques rencontrée au cours du cycle de fonctionnement de la structure est prise en compte. La modélisation permet d’évaluer l’impact des conditions opératoires sur la tenue mécanique de la structure. / Technologies using high temperature oxygen transport through mixed conductor materials undergo thermal andchemical expansions. The industrial structures suffer from thermo-chemo-mechanical stresses which may be modeled to predict their mechanical reliability. This work is a step toward the development of design tools for mechanics of structure made of mixed conductor. The goal is to deal with measurable parameters such as temperature and oxygen partial pressure. The first aim is to provide a realistic macroscopic modelling of chemical expansion. The second one is to model the coupling between mechanics, oxygen transport and heat transfer. The oxygen bulk diffusion is described following the Wagner theory. The kinetics of surface exchange and their consequences in terms of chemo-mechanical shocks have been explored. In order to conduct computation of complex structures in three dimensions with steady and transient state, the models have been implemented in finite element analysis software (Abaqus). Comparison with analytical results is also reported. Finally, a semi-industrial catalytic membrane reactor for partial oxidation of methane to syngas is computed. The modelling helps to analysed the impact of operating conditions on the mechanical reliability of the whole structure.

xvii, 159 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Experimental studies on mix-conducting hetero-ionic junctions of anionically (PA A ) and cationically (PA C ) functionalized polyacetylene ionomers, as well as each individual ionomer, in thin-film sandwich configurations are reported for the purpose of better understanding the interaction between ionic and electronic charge transports in mixed ionic-electronic conductor (MIEC) systems. The transport of ions in both individual ionomers as well as their hetero-ionic junction was investigated via small-amplitude AC impedance spectroscopy in the absence of significant interference from the electronic charge transport. Modeling of the impedance results reveal important information about the materials such as: ion conductivity, activation energy of ion conduction, ion hopping frequency, dielectric constant, interfacial capacitance, and estimates of effective ion density. Electrochemical injection of electronic charge carriers into PA A and PA C from gold electrodes was monitored to determine the applied potentials needed to drive hole and electron injection into each ionomer. It is found that for both ionomers, the onset voltages for unipolar and bipolar charge injection are similar, and holes can be injected at close to zero bias. The responses of the complete Au|PA A |PA C |Au hetero-ionic junction, as well as each constituent ionomer layer in Au|Ionomer|Au configuration, to various stepping biases were investigated through current-voltage and impedance measurements to study the origin of the asymmetric current-voltage response observed in the hetero-ionic junction. Analysis of the results reveal a working mechanism of a mix-conducting junction that is fundamentally different from that of a purely electronic pn junction. When illuminated with light, the Au|PA A |PA C |Au junction exhibits unidirectional photovoltage and photocurrent with the PA A side at higher potential, while the Au|PA A |Au and Au|PA C |Au samples exhibit symmetric photoresponses. The efficiency of photocurrent generation in the Au|PA A |PA C |Au junction was found to be strongly dependent on the direction of illumination and on the sample thickness. These observations can be explained by the difference in the mobility of holes and electrons and the existence of a built-in ionic space charge region at the PA A |PA C interface. A mechanism of photoresponse unique to MIEC junctions was proposed, and the magnitude of built-in potential was estimated. / Committee in charge: J David Cohen, Chairperson, Physics; Mark Lonergan, Advisor, Chemistry; Roger Haydock, Member, Physics; David Strom, Member, Physics; David Tyler, Outside Member, Chemistry

Orientador: Rafael Zadorosny / Resumo: Neste trabalho é apresentada a produção de condutores revestidos de material supercondutor (superconducting coated conductors – SCC), ou seja, um filme supercondutor cerâmico, obtido por impressão direta da solução precursora sobre um substrato. Este processo foi estudado com o intuito de aplicar uma técnica de fabricação simples e de baixo custo visando a obtenção de filmes de boa qualidade a um custo reduzido. As soluções precursoras de CeO2, BSCCO e YBCO foram obtidas pelo método Pechini, considerada uma rota de produção de baixo custo. A fim de comparar a impressão direta com outra técnica, foram produzidos os mesmos filmes por spin coating. Para se obter os SCC, foi adicionada Ag às soluções dos materiais cerâmicos verificando sua incorporação na estrutura do filme e não apenas como um material de revestimento (como ocorre com as fitas supercondutoras de segunda geração). As caracterizações morfológicas e estruturais foram realizadas para identificar e analisar o processo de impressão direta do SCC. Já o comportamento supercondutor do material foi verificado através de medidas de R x T. / Abstract: This work presents the production of superconducting coated conductors (SCC), that is, a superconducting ceramic film obtained by direct printing of the precursor solution on a substrate. This process was studied with the intention of applying a simple and low cost technique focusing in the obtaining of good quality films at a reduced cost. The precursor solutions of CeO2, BSCCO and YBCO were obtained by the Pechini method, also considered a low cost production route. In order to compare direct printing with another technique, the same films were produced by spin coating. In order to obtain the SCC's, Ag was added to the solutions of the ceramic materials to incorporate in the film structure and not just as a coating material (as with second-generation superconducting tapes). Morphological and structural characterizations were performed to identify and analyze the SCC obtained by direct printing process. The superconductive behavior of the material was verified by measurements of R x T. / Doutor

Deux systèmes de spins uniques sont étudiés dans cette thèse : d’abord un unique atome de Mn dans une boîte quantique chargée positivement, puis un unique atome de Cr dans une boîte quantique neutre. Cette étude a été entièrement réalisée par des moyens optiques, via la photoluminescence d’une boîte unique. Ces deux systèmes sont fortement couplés aux phonons et aux contraintes. Ce couplage permet de ne plus se limiter à une détection et une manipulation du spin optique, mais ouvre également la possibilité de le faire en modulant le champ de contrainte.Par des expériences de photoluminescence résonante, nous montrons l’existence de niveaux optique en Λ dans les boîtes quantiques chargées positivement et dopées d’un unique atome de Mn. Ces niveaux en Λ sont utilisés pour étudier la dynamique du spin hybride trou-Mn. Cette étude révèle l’existence de flip-flops des spins du trou et du Mn à l’échelle de la nanoseconde, dus à l’interaction d’échange trou-Mn et à l’interaction avec les phonons acoustiques. Un couplage par l’anisotropie des contraintes dans le plan de niveaux électron-Mn dégénérés et séparé par un spin flip de deux unités est aussi démontré, et dynamique cohérente induite par les contraintes est étudiée en détail.Grâce à des expériences magnéto-optiques, nous avons pu détecter la photoluminescence d’un atome de Cr unique dans une boîte quantique, et extraire une anisotropie magnétique du spin du Cr de quelques meV. De nombreux paramètres des boîtes étudiées peuvent être extrait de ces expériences, et nous montrons notamment que le couplage trou-Cr est antiferromagnétique. Nous démontrons que le spin du Cr peut être préparé par pompage optique résonant. Ces expériences ont permis de montrer que, sous excitation, le spin du Cr fait des flip-flops avec celui du trou, causé par l’interaction d’échange trou-Cr et le couplage aux phonons acoustiques. Ces flip-flops causent une relaxation rapide du spin du Cr sous excitation, mesurée comme de l’ordre de quelques dizaines de nanosecondes. Dans le noir, nous avons trouvé que le spin du Cr relaxe en quelques microsecondes. Finalement, nous avons aussi démontré la possibilité de contrôler le spin du Cr par l’effet Stark optique. / Two different single spin systems are studied in this thesis: single Mn spin in positively charged quantum dots, and single Cr atom in a neutral quantum dots. Both are probed optically, using the photoluminescence of a single dot. Both systems are strongly coupled to phonons and strains. This coupling opens new ways to probe and control the spins of the magnetic atoms, not only optically, but also by modulating the strain state at their position.Using resonant photoluminescence, we demonstrate the existence of optical Λ-level systems in Mn-doped positively charged quantum dots, and use them to study the dynamics of the hole-Mn hybrid spin. It reveals hole-Mn spin flip-flops in the nanosecond range due to the interplay of the interaction with acoustic phonons and the hole-Mn exchange interaction. We also show that degenerated electron-Mn states separated by spin flips of two units are coupled through the in-plane strain anisotropy, and study this strain induced coherent dynamics.Using magneto-optic experiments, we are able to probe the spin of a single Cr atom and extract a magnetic anisotropy D0 in the meV range. Several parameters of the QD are extracted from these experiments, and, especially, we show that the h-Cr coupling is anti-ferromagnetic. We demonstrate that the Cr spin can be prepared using resonant optical pumping. These experiments evidence a Cr relaxation time under excitation in the 10 nanoseconds range. This relaxation is driven by hole-Cr spin flip-flops caused by the interplay of the interaction with acoustic phonons and the hole-Cr exchange interaction. A relaxation in the dark in the microseconds range was also measured. Possibility of control of the Cr spin was also demonstrated using the optical Stark effect.

CAPES / Com o avanço da miniaturização de componentes e dispositivos eletrônicos ocorrida nos últimos anos, a utilização de materiais dielétricos e a necessidade de informações precisas sobre o comportamento dielétrico apresentado por estes materiais aumentou consideravelmente. Neste trabalho é apresentado inicialmente as motivações para o estudo do comportamento dielétrico e da modelagem da função resposta dielétrica. A partir da teoria proposta por Debye e identificando suas peculiaridades, são exploradas algumas extensões deste modelo e analisada a interpretação da função resposta proposta por estes. Muitos modelos assumiam a existência de múltiplas interações envolvendo os dipolos com o meio dielétrico, as quais contribuíam para a dinâmica do comportamento dielétrico, somente mais tarde é que estas múltiplas interações ganharam uma conexão entre a resposta dielétrica observada com as propriedades intrínsecas do material. Por meio do modelo proposto por Dissado e Hill e assumindo dados experimentais disponíveis na literatura para alguns materiais, foi testada a validade da função resposta resultante do modelo, na qual veri cou-se a capacidade da mesma em ajustar as curvas para as componentes real e imaginária da permissividade para uma grande variedade de materiais dielétricos. A partir das simulações e análises realizadas, ficou evidente a dependência do comportamento dielétrico com a temperatura, fato este que deverá ser abordado em trabalhos futuros. / With the improvement of miniaturization of electronic components and devices occurred in recent years, the use of dielectric materials and the need for accurate information about the dielectric behavior displayed by these materials has increased considerably. In this work is initially presented the motivations for the study of dielectric behavior and the modeling of the dielectric response function. From the theory proposed by Debye and identifying its peculiarities, are exploited some extensions of this model and analyzed the interpretation of response function proposed by these. Many models used to assume the existence of multiple interactions involving the dipoles with the dielectric medium, which contributed to the dynamics of the dielectric behavior, only later the multiple interactions won a connection between the dielectric response observed with the intrinsic properties of the materials. Through the model proposed by Dissado and Hill and assuming experimental data available in bibliography for some materials, was tested the validity of the response function resulting from the model, in which was veri ed the ability of the same to adjust the curves for the real and imaginary components of permittivity to a wide variety of dielectric materials. From the simulations and analyzes performed, was evident the dependence of dielectric behavior with temperature, a fact that should be discussed in future works.

Resumo: O trabalho busca trazer uma contribuição na utilização da energia elétrica, através do melhor uso das lâmpadas de descarga à alta pressão, de vapor de mercúrio e de sódio. Dois aspectos são tratados: a influência deste tipo de lâmpada na qualidade de energia, uma vez que esta avaliação é difícil, por se tratar de uma carga distribuída por toda a cidade e o aspecto do dimensionamento dos condutores para os circuitos que têm uma alimentação exclusiva através de transformadores dedicados. A parte prática do trabalho está baseada em experimentos e medições feitas em uma subestação experimental montada no Laboratório de Alta Tensão na UNESP, campus de Guaratinguetá. Através de oscilografia, as formas de ondas de corrente e tensão, no lado de baixa tensão e média tensão, foram medidas, analisadas e avaliadas. Com a utilização de softwares gráficos foram comparadas as formas de ondas mostradas pelo equipamento com as curvas traçadas a partir de valores calculados. Foram avaliadas as influências dos transformadores de corrente e dos transformadores de potencial sobre as medições dos parâmetros elétricos de uma instalação. / Abstract: The work wants to give a contribution in the use of the electric power, trough the best use of the high pressure discharge lamps, of mercury and sodium. Two aspects are treated: the lamp type influence in Energy Quality, once this evaluation is difficult, for treating of a load distributed by the whole city, and the aspect of the dimensioning of the feeders for circuits that have and exclusive feeding through transformers.A brief revision of lighting concepts is made and also a study of harmonic current is presented. It was looked for, in research, to know the state of the art for the subject. The practical part of work is based on experiments and measurements made in a mounted experimental substation in UNESP High Tension Laboratory, campus of Guaratinguetá. Through oscilograph voltage and current waves formats, in low and high voltage sides, they were measured, analyzed and appraised. With utilization of graphics software was a made a comparison between the equipment oscilographed curves and curves acquire on calculated values. They were appraised the influences of voltage and current transformers about the measurents of the electric parameters of an installation. / Orientador: Oscar Armando Maldonado Astorga / Coorientador: José Luz Silveira / Banca: Agnelo Marotta Cassula / Banca: José Policarpo Gonçalves de Abreu / Mestre

Made available in DSpace on 2014-06-11T19:29:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-12-21Bitstream added on 2014-06-13T18:59:49Z : No. of bitstreams: 1 damato_jc_me_guara.pdf: 907873 bytes, checksum: 1173d249b00c8dc682ed7ae9dce890c3 (MD5) / Universidade Estadual Paulista (UNESP) / O trabalho busca trazer uma contribuição na utilização da energia elétrica, através do melhor uso das lâmpadas de descarga à alta pressão, de vapor de mercúrio e de sódio. Dois aspectos são tratados: a influência deste tipo de lâmpada na qualidade de energia, uma vez que esta avaliação é difícil, por se tratar de uma carga distribuída por toda a cidade e o aspecto do dimensionamento dos condutores para os circuitos que têm uma alimentação exclusiva através de transformadores dedicados. A parte prática do trabalho está baseada em experimentos e medições feitas em uma subestação experimental montada no Laboratório de Alta Tensão na UNESP, campus de Guaratinguetá. Através de oscilografia, as formas de ondas de corrente e tensão, no lado de baixa tensão e média tensão, foram medidas, analisadas e avaliadas. Com a utilização de softwares gráficos foram comparadas as formas de ondas mostradas pelo equipamento com as curvas traçadas a partir de valores calculados. Foram avaliadas as influências dos transformadores de corrente e dos transformadores de potencial sobre as medições dos parâmetros elétricos de uma instalação. / The work wants to give a contribution in the use of the electric power, trough the best use of the high pressure discharge lamps, of mercury and sodium. Two aspects are treated: the lamp type influence in Energy Quality, once this evaluation is difficult, for treating of a load distributed by the whole city, and the aspect of the dimensioning of the feeders for circuits that have and exclusive feeding through transformers.A brief revision of lighting concepts is made and also a study of harmonic current is presented. It was looked for, in research, to know the state of the art for the subject. The practical part of work is based on experiments and measurements made in a mounted experimental substation in UNESP High Tension Laboratory, campus of Guaratinguetá. Through oscilograph voltage and current waves formats, in low and high voltage sides, they were measured, analyzed and appraised. With utilization of graphics software was a made a comparison between the equipment oscilographed curves and curves acquire on calculated values. They were appraised the influences of voltage and current transformers about the measurents of the electric parameters of an installation.