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1	Agglomeration and collection of fine secondary phases in flowing suspensions utilizing resonant ultrasonic fields Tolt, Thomas Lester 09 June 2003 (has links) No description available.
2	Annealing of Cu2ZnSn(S,Se)4 Thin Films : A Study of Secondary Compounds and Their Effects on Solar Cells Ren, Yi January 2017 (has links) Kesterite Cu2ZnSnS4 (CZTS) is interesting as a sustainable photovoltaic technology due to its earth-abundant elements and suitable semiconducting properties. To date, a record efficiency of 12.6% has been achieved but further improvements are required to reach high efficiency for industrial implementation. Among the limiting issues is the understanding of the annealing process, which is crucial in promoting high material quality. In particular, the knowledge of the effects of segregated secondary compounds on solar cell performance is lacking. In contrast to formation of ZnS particles throughout CZTS film, it is notable that SnS forms and usually segregates on the CZTS top and rear surfaces. The influence of SnS on CZTS solar cells was studied by electron beam induced current measurements. It is found that SnS presence on the CZTS surfacecan introduce “dead area”, whereas it seems beneficial for solar cell current when accumulates on the CZTS rear. For SnS passivation and from investigation of the passivation effect from an Al2O3 thin layer at the CZTS rear, improvement in overall device performance could not be demonstrated, due to either poor CZTS bulk or non-optimal device structure. The limitation in CZTS bulk quality was shown from a thickness study where carrier collection saturated already about 700-1000 nm CZTS thickness. Formation of SnS alongside CZTS implies the anneal is limited by a deficient sulfur partial pressure (PS2). By looking into Sn-S phase transformations in SnS2 films after annealing, we find that PS2 drops rapidly over the annealing time, which could be well-correlated to a series of changes in CZTS material quality including secondary phase formations and defect modifications. It is shown that annealing CZTS under sufficiently high PS2 is critical for CZTS solar cells with high open circuit voltage (upto 783mV was reached), possibly due to the defect modification. Besides SnS, it is observed that NaxS compounds are also readily formed on CZTS surfaces, due to Na diffusion from the glass substrate during annealing. NaxS negatively affects the formation of the CdS/CZTS interface during chemical bath deposition. It can be removed by an oxidation process or wet chemical etching. Annealing sputtering thin film CZTS secondary phases solar cell Engineering and Technology Teknik och teknologier
3	Propriedades estruturais e controle da estequiometria de filmes finos de BiFeO3 / Sena, Wellington Adriano Fernandes January 2019 (has links) Orientador: Eudes Borges de Araújo / Resumo: O objetivo do trabalho foi estudar as propriedades estruturais dos filmes finos de ferrita de bismuto (BFO) ao se adicionar excesso de nitrato de ferro ao invés de nitrato de bismuto conforme muitas referências na literatura vêm praticando com a intenção de obter um BFO puro. Filmes finos de BFO foram preparados sobre substratos Pt/TiO2/SiO2/Si(100) usando o método de Pechini pertencente a rota química sol-gel polimérica. Foram produzidos filmes de estequiometria nominal e de variação de 2, 4, 6, 8, 10 e 12 mol% de excesso de nitrato de Ferro. O processo de síntese dos filmes passou por quatro deposições, quatro pirólises a 300 ºC por 20 minutos e cristalização a 600 ºC por 40 minutos. As propriedades físicas dos filmes foram investigadas usando técnicas de MEV, DRX, Raman e EDS. Rietveld foi usado para calcular os parâmetros de rede e o modelo de Williamson-Hall foi usado para calcular o tamanho do cristalito e o microstrain. Resultados do DRX revelaram o aparecimento da fase secundária Bi2O3, ela aparece quando há o excesso de bismuto. Resultados do EDS confirmam o excesso de Bi. A técnica de EDS apontou uma maior At% do bismuto em relação ao ferro em todas as amostras, sendo que, a de 12 mol% foi a que apresentou características mais próxima de uma estequiometria desejável para a produção de um BFO puro. / Abstract: The objective of this work was to study the structural properties of bismuth ferrite (BFO) thin films by adding excess iron nitrate instead of bismuth nitrate as many references in the literature have been practicing with the intention of obtaining a pure BFO. BFO thin films were prepared on Pt / TiO2 / SiO2 / Si (100) substrates using the Pechini method belonging to the polymeric sol-gel chemical route. Films of nominal stoichiometry and variation of 2, 4, 6, 8, 10 and 12 mol% of iron nitrate excess were produced. The synthesis process of the films went through four depositions, four pyrolysis at 300 ºC for 20 minutes and crystallization at 600 ºC for 40 minutes. The physical properties of the films were investigated using SEM, XRD, Raman and EDS techniques. Rietveld was used to calculate lattice parameters and the Williamson-Hall model was used to calculate crystallite size and microstrain. XRD results revealed the appearance of the secondary phase Bi2O3, it appears when there is excess bismuth. EDS results confirm excess Bi. The EDS technique showed a higher At% of bismuth in relation to iron in all samples, and the 12 mol% was the one that presented characteristics closer to a desirable stoichiometry for the production of a pure BFO. / Mestre Filmes finos. Ferrita de bismuto Fases secundárias Filmes finos ferroelétricos. Bismuth ferrite Secondary phases
4	Développement des bases théoriques nécessaires à la modélisation de la vitesse résiduelle d'altération en milieu aqueux des verres nucléaires AVM. / Development of basis necessary to model the aqueous residual alteration rate of AVM nuclear glasses Thien, Bruno 03 December 2010 (has links) En milieu aqueux, les verres nucléaires AVM présentent de grandes différences de comportement à l'altération, malgré de faibles variations de composition. La vitesse résiduelle d'altération de ces verres est contrôlée par deux phénomènes, qui sont la précipitation de phases secondaires de type hectorites alumineuses, qui en altérant le gel protecteur, augmentent la vitesse résiduelle d'altération du verre, et, la diffusion de l'eau à travers un gel plus ou moins protecteur. Le magnésium, contenu dans ces verres, facilite la précipitation de ces phases secondaires, mais s'incorpore également dans le gel, augmentant son pouvoir de passivation. La prédominance de l'un ou l'autre de ces phénomènes dépend de la composition initiale du verre, du pH de la solution, des conditions d'altération. Altérés en eau souterraine de stockage (riche en Mg et Ca), les verres AVM s'altèrent moins qu'en eau pure, et ce malgré la précipitation de phases secondaires. Le calcium s'incorpore dans le gel, à la place du sodium et du magnésium, augmentant son pouvoir de passivation. Nous avons adapté le modèle géochimique d'altération des verres GRAAL, aux verres AVM. Malgré ses limites, ce modèle nous permet de rendre compte des différences de comportement entre les verres AVM, selon leur composition, ainsi que de proposer un modèle opérationnel de l'altération des verres AVM. / During their aqueous alteration, AVM French nuclear glasses exhibit a large range of behaviour, in spite of a small range of composition. AVM glasses alteration rates are controlled by two phenomena: (i) precipitation of secondary phases, mostly aluminous hectorites, and (ii) diffusion of water across a more or less protective gel. The magnesium contained in these glasses increases the precipitation of these secondary phases, leading to a partial or total dissolution of the gel layer. This dissolution increases the glass alteration rates. On the other hand, Mg also incorporates in the gel, increasing his passivation properties. The predominance of one of these two phenomena depends on the initial composition of the glass, the pH of the solution, and the alteration conditions. In presence of Bure geological disposal site water (Mg and Ca rich), AVM glasses undergo less alteration than in initially pure water, in spite of larger amounts of secondary phase precipitates. This results from incorporation of calcium in the gel instead of sodium and magnesium, improving its passivating properties. We have adapted the geochemical GRAAL model for AVM glasses. In spite of its limitations, this model allows us to describe the differences of behaviour between these glasses, in function of their composition. Moreover, GRAAL can be proposed as a basis of a future operational model for predicting the alteration of AVM glasses. Verres nucléaires AVM Smectite Hectorite Diffusion Modélisation Phases secondaires AVM nuclear glasses Smectite Hectorite Diffusion Model Secondary phases
5	Microscopic Characterisation of Solar Cells : An Electron Microscopy Study of Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 Solar Cells Wätjen, Jörn Timo January 2013 (has links) The sun provides us with a surplus of energy convertible to electricity using solar cells. This thesis focuses on solar cells based on chalcopyrite (CIGSe) as well as kesterite (CZTS(e)) absorber layers. These materials yield record efficiencies of 20.4 % and 11.1 %, respectively. Especially for CZTS(e), the absorber layers often do not consist of one single desired phase but can exhibit areas with deviating material properties, referred to as secondary phases. Furthermore, several material layers are required for a working solar cell, each exhibiting interfaces. Even though secondary phases and interfaces represent a very small fraction of the solar cell they can have a profound influence on the over-all electrical solar cell characteristics. As such, it is crucial to understand how secondary phases and interfaces influence the local electrical characteristics. Characterising secondary phases and interfaces is challenging due to their small sample volume and relatively small differences in composition amongst others. This is where electronmicroscopy, especially transmission electron microscopy, offers valuable insight to material properties on the microscopic scale. The main challenge is, however, to link these material properties to the corresponding electrical characteristics of a solar cell. This thesis uses electron beam induced current imaging and introduces a new method for JV characterisation of solar cells on the micron scale. Combining microscopic structural and electrical characterisation techniques allowed identifying and characterising local defects found in the absorber layer of CIGS solar cells after thermal treatment. Furthermore, CZTSe solar cells in this thesis exhibited a low photo-current density which is traced to the formation of a current blocking ZnSe secondary phase at the front contact interface. The electron microscopy work has contributed to an understanding of the chemical stability of CZTS and has shown the need for an optimised back contact interface in order to avoid chemical decomposition reactions and formation of detrimental secondary phases. With this additional knowledge, a comprehensive picture of the material properties from the macroscopic down to the microscopic level can be attained throughout all required material layers. TEM SEM FIB solar cell CIGS CZTS Alternative buffer layers Gallium gradients microscopic electrical characterisation Secondary Phases
6	Efeito dos métodos de síntese e sinterização na densificação, estrutura, microestrutura e condutividade elétrica do galato de lantânio / Effects of the synthesis and sintering methods on the densification, structure, microstructure and electrical conductivity of doped lanthanum gallate Reis, Shirley Leite dos 17 July 2014 (has links) O galato de lantânio contendo substituições parciais de estrôncio e magnésio (La1-xSrxGa1-yMgyO3-δ) apresenta estrutura tipo perovsquita e alta condutividade para íons de oxigênio. Outras características desta cerâmica são o extenso domínio eletrolítico e a baixa condutividade eletrônica. É um material promissor para uso como eletrólito sólido em células a combustível de óxido sólido que operam em temperaturas intermediárias, devido sua alta condutividade iônica e estabilidade em uma ampla faixa de pressão parcial de oxigênio. Neste trabalho, a composição La0,9Sr0,1Ga0,8Mg0,2O3-δ foi preparada pelo método convencional de mistura de óxidos a partir de diferentes rotas e pelo método de complexação de cátions. As amostras foram consolidadas pelo método convencional de sinterização e por sinterização rápida. Pelo método de mistura de óxidos foi possível obter a fase ortorrômbica do LSGM, mas não foi possível eliminar as fases SrLaGaO4, La4Ga2O9 e SrLaGa3O7, independente das condições de sinterização utilizadas. Precipitados de óxido de magnésio foram observados nas amostras preparadas pelos dois métodos de síntese empregados identificados apenas por microscopia eletrônica de varredura. As densidades obtidas foram superiores a 97% da densidade teórica em amostras sinterizadas a 1450 °C/4 h, para os materiais preparados por mistura de óxidos. Amostras preparadas por método de complexação de cátions e aquelas consolidadas por sinterização rápida apresentaram menores valores de densidade. Grãos de tamanhos micrométricos foram obtidos para os dois métodos de sinterização. Amostras calcinadas a 1250°C apresentaram maiores densidades e maiores valores de condutividade iônica dos grãos e dos contornos de grãos, quando comparadas com as demais amostras. / Lanthanum gallate with partial substitution on La and Ga sites (La1-xSrxGa1-yMgyO3-δ) has perovskite structure and high oxide-ion conductivity. Other properties of this ceramic material comprise a relatively wide electrolytic domain and low electron conductivity. Doped lanthanum gallate is a potential solid electrolyte for intermediate-temperature solid oxide fuel cells due to its high ionic conductivity and stability in a wide range of oxygen partial pressure. In this work, the composition La0.9Sr0.1Ga0.8Mg0.2O3-δ was prepared by the conventional method of mixing of the starting oxides followed by different processing routes and by the cation complexation method. The ceramic specimens were consolidated by conventional sintering and by fast firing. All specimens prepared by solid state reaction show the characteristic orthorhombic phase of lanthanum gallate and SrLaGaO4, La4Ga2O9 and SrLaGa3O7 secondary phases, independent on the method of sintering. Energy dispersive X-ray spectroscopy coupled to scanning electron microscopy evidenced that all prepared specimens contain MgO grains precipitated along the grain boundaries. High relative densities were obtained for specimens prepared by solid state reaction and consolidated by conventional sintering at 1450 °C/4 h. All specimens exhibit micron sized grains independent on the sintering method. The highest values of relative density and ionic conductivity were obtained for specimens calcined at 1250°C. cation complexation technique complexação de cátions conventional sintering fases secundárias fast firing galato de lantânio lanthanum gallate mistura de óxidos secondary phases sinterização convencional sinterização rápida solid state reaction
7	Efeito dos métodos de síntese e sinterização na densificação, estrutura, microestrutura e condutividade elétrica do galato de lantânio / Effects of the synthesis and sintering methods on the densification, structure, microstructure and electrical conductivity of doped lanthanum gallate Shirley Leite dos Reis 17 July 2014 (has links) O galato de lantânio contendo substituições parciais de estrôncio e magnésio (La1-xSrxGa1-yMgyO3-δ) apresenta estrutura tipo perovsquita e alta condutividade para íons de oxigênio. Outras características desta cerâmica são o extenso domínio eletrolítico e a baixa condutividade eletrônica. É um material promissor para uso como eletrólito sólido em células a combustível de óxido sólido que operam em temperaturas intermediárias, devido sua alta condutividade iônica e estabilidade em uma ampla faixa de pressão parcial de oxigênio. Neste trabalho, a composição La0,9Sr0,1Ga0,8Mg0,2O3-δ foi preparada pelo método convencional de mistura de óxidos a partir de diferentes rotas e pelo método de complexação de cátions. As amostras foram consolidadas pelo método convencional de sinterização e por sinterização rápida. Pelo método de mistura de óxidos foi possível obter a fase ortorrômbica do LSGM, mas não foi possível eliminar as fases SrLaGaO4, La4Ga2O9 e SrLaGa3O7, independente das condições de sinterização utilizadas. Precipitados de óxido de magnésio foram observados nas amostras preparadas pelos dois métodos de síntese empregados identificados apenas por microscopia eletrônica de varredura. As densidades obtidas foram superiores a 97% da densidade teórica em amostras sinterizadas a 1450 °C/4 h, para os materiais preparados por mistura de óxidos. Amostras preparadas por método de complexação de cátions e aquelas consolidadas por sinterização rápida apresentaram menores valores de densidade. Grãos de tamanhos micrométricos foram obtidos para os dois métodos de sinterização. Amostras calcinadas a 1250°C apresentaram maiores densidades e maiores valores de condutividade iônica dos grãos e dos contornos de grãos, quando comparadas com as demais amostras. / Lanthanum gallate with partial substitution on La and Ga sites (La1-xSrxGa1-yMgyO3-δ) has perovskite structure and high oxide-ion conductivity. Other properties of this ceramic material comprise a relatively wide electrolytic domain and low electron conductivity. Doped lanthanum gallate is a potential solid electrolyte for intermediate-temperature solid oxide fuel cells due to its high ionic conductivity and stability in a wide range of oxygen partial pressure. In this work, the composition La0.9Sr0.1Ga0.8Mg0.2O3-δ was prepared by the conventional method of mixing of the starting oxides followed by different processing routes and by the cation complexation method. The ceramic specimens were consolidated by conventional sintering and by fast firing. All specimens prepared by solid state reaction show the characteristic orthorhombic phase of lanthanum gallate and SrLaGaO4, La4Ga2O9 and SrLaGa3O7 secondary phases, independent on the method of sintering. Energy dispersive X-ray spectroscopy coupled to scanning electron microscopy evidenced that all prepared specimens contain MgO grains precipitated along the grain boundaries. High relative densities were obtained for specimens prepared by solid state reaction and consolidated by conventional sintering at 1450 °C/4 h. All specimens exhibit micron sized grains independent on the sintering method. The highest values of relative density and ionic conductivity were obtained for specimens calcined at 1250°C. complexação de cátions fases secundárias galato de lantânio mistura de óxidos sinterização convencional sinterização rápida cation complexation technique conventional sintering fast firing lanthanum gallate secondary phases solid state reaction
8	Altération aqueuse et hydratation en phase vapeur du verre SON68 à basse température (35-90°C) / Aqueous and water vapour alteration of the SON68 glass at low temperature (35-90°C) Bouakkaz, Rachid 24 September 2014 (has links) Le verre SON68 est dans un premier temps altéré en mode dynamique dans l’eau de COx riche en silicium (42mg/L) à pH 8, à fort S/V (14000 m⁻¹) et à 35, 50 et 90°C. Les résultats montrent que l’altération du verre semble être gouvernée par un mélange de processus de diffusion et de réaction de surface. La vitesse résiduelle à 90°C est de l’ordre de 10⁻⁴ g.m⁻².j⁻¹, l’énergie d’activation est de l’ordre de 70 kJ.mol⁻¹. Un mécanisme de dissolution/précipitation et d’hydrolyse/condensation sont responsables du développement de la couche d’altération. Les silicates de Mg et la calcite précipitent à 35 et 50°C, mais en plus la powellite et l’apatite ont été identifiées à90°C. Les résultats de la modélisation géochimique reproduisent les données expérimentales. Le verre est ensuite hydraté à des températures allant de 35 à 125°C et des valeurs d’humidité relative (HR) entre 92 et 99,9%. L’hydratation du verre augmente avec la température et l’HR. L’énergie d’hydratation est de l’ordre de 34,2 kJ.mol⁻¹. Les épaisseurs des couches d’altération varient entre 0,3μm à 35°C et 5μm à 125°C. La couche d’altération est appauvrie en (B, Li, Na) et enrichie en (Si, Al, Fe, Ca, Zn et Ni). Les principales phases secondaires formées sont la calcite, la powellite, l’apatite, la tobermorite et un gel hydraté.L’influence des matériaux en champ proche sur l’altération du verre SON68 dopé en ²⁹Si a été étudiée. La présence d’acier augmente le pH et diminue la concentration en Si et en Mo sans modifier la vitesse globale de corrosion du verre. Le Si est retenu sur les produits de corrosion d’acier, sa concentration en solution semble être contrôlée par la dissolution de l’argilite. La corrosion du verre en présence d’acier et d’argile à 90°C conduit à la formation de magnétite, sidérite, ferrosilicates, silice pure, sulfures de fer (pyrite, troïlite, pyrrhotite etmackinawite), calcite, apatite, powellite et silicates de Mg. Les résultats de modélisation sont en bon accord avec les données expérimentales. / The SON68 glass is initially altered in dynamic mode under silica rich COx water (42 mg/L) at pH8, high S/V ratio (14000 m⁻¹) and at 35, 50 and 90°C. The results showed that the glass alteration seems to be governed by both diffusion and surface reaction process. The residual rate at 90°C is around 10-4 g.m⁻².d⁻¹. The activation energy is about 70 kJ.mol⁻¹. The dissolution /precipitation and hydrolysis/condensation mechanisms are responsible for the development of the alteration layer. Mg silicates and calcites precipitate at 35 and 50°C, the same phases in addition to powellite and apatite precipitate at 90°C. The results predicted by the model reproduce well experimental data. The glass is then hydrated at temperatures ranging from 35 to 125°C and relative humidity values (RH) between 92 an 99.9%. The glass hydration increases with the temperature and RH, the hydration energy is about 34.2 kJ.mol⁻¹. The alteration layers thicknesses vary between 0.3μm at 35°C and 5μm at 125°C. The alteration layer is depleted in (B, Li, Na) and enriched in (Si, Al, Fe, Zn and Ni). The secondary phases are calcite, powellite, apatite and tobermorite in adition to a hydration gel. The effect of near field materials on the ²⁹Si doped SON68 glass alteration was studied. The presence of steel increases the pH and decreases the Si and Mo concentrations without changing the overall rate of glass corrosion. The Si is retained on the steel corrosion products, its concentration in solution seems to be controlled by the clay dissolution. The glass corrosion in the presence of steel and clay at 90°C leads to the formation of magnetite, siderite, ironsilicates, pure silica, iron sulphur (pyrite, troilite,pyrrhotite and mackinawite), calcite, apatite, powellite and Mg silicates. The modelling results agree well with the experimental data. Verre nucléaire SON68 Corrosion Phases secondaires Hydratation Cellules de percolation Matériaux en champ proche Spectroscopie Raman Isotopie (29Si, D2O18) Modélisation géochimique Nuclear glass SON68 Corrosion Secondary phases Hydration Percolation cells Near field materials Raman spectroscopy Isotopy (29Si, D2O18) Geochemical modelling
9	Performance characterisation of duplex stainless steel in nuclear waste storage environment Ornek, Cem January 2016 (has links) The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis. 620.1
10	Structural and optical impact of transition metal implantation into zinc oxide single crystals and nanowires / Strukturelle und optische Auswirkungen derÜbergangsmetallimplantation in ZnO Einkristalle und Nanodrähte Müller, Sven 30 March 2009 (has links) No description available. 530 Physik Mathematics and Computer Science Nanodraht Zinkoxid Photolumineszenz Kathodolumineszenz Ionenimplantation Leuchtzentren Dotierung Übergangsmetalle Eisen Nickel Mangan Kobalt Vanadium interstitieller Sauerstoff interstitielles Zink grünes Lumineszenzband rot-gelbes Lumineszenzband intra-3d Lumineszenz Zweiphasen Raman Röntgenbeugung nanowire zinc oxide photoluminescence cathodoluminescence ion implantation color center doping transition metals iron nickel manganese cobalt vanadium interstitial oxygen interstitial zinc green luminescence band red-yellow luminescence band intra-3d-shell luminescence secondary phases raman X-ray diffraction 33.07 33.61 33.72 RVC 520: Gitterschwingungen RVQ 000: Halbleiter {Physik}

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