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Brown, Jared C. "UV Visible Spectra Analysis of High Temperature Water Gas Shift Catalysts Made from Iron, Lanthanum, Copper, and Chromium Oxides." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3222.
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Hydrogen is a vital component in several different chemical reactions as well as a potential fuel source for the future. The water gas shift (WGS) reaction converts CO and water to hydrogen and CO2. The objective of this work is to first, characterize the potential benefits of the addition of lanthanum oxide (lanthana) to the iron-chromium-copper (Fe-Cr-Cu) oxide catalysts industrially used in high temperature water gas shift processes, and second, analyze these catalysts using in-situ UV-Visible spectroscopy. The benefits of each component in the catalyst are discussed as well as potential benefits from the addition of lanthana. Lanthana is a rare earth oxide that dramatically increases the surface area of the iron based WGS catalysts, and small concentrations of other rare earth oxides (i.e. cerium) have been shown to increase the rate of desorption of CO2 from iron surfaces (Hu Yanping 2002). Lanthana has similar chemical properties to other rare earth oxides tested and has not been previously tested as an additive to the WGS catalyst. Therefore catalysts with 0, 1, 2, 5, 10, and 20 wt% lanthana were made via a co-precipitation method in order to measure changes in activity, physical stability, and thermal stability. Catalyst characterization techniques utilized include electron dispersive X-ray spectroscopy (EDX), temperature programmed reduction (TPR) with hydrogen, and nitrogen physisorption (BET). The kinetic analysis was performed utilizing both mass spectroscopy (MS) and gas chromatography (GC). The addition of 1 wt% lanthana to the Fe-Cr-Cu catalysts increases WGS reaction rates of the catalyst at 425°C and 350°C, however the 0% La catalyst has the highest rates at 375°C and 400°C. The 0% La catalyst shows significant drop off in rate at 425°C, suggesting that the lanthana provides a small thermal stabilizing, i.e. the addition of lanthana prevents catalyst sintering at higher temperatures. Traditionally, chromia acts as the sole thermal stabilizer in these catalysts. The addition of large amounts of lanthana inhibits the chromia stabilizing effect, however small additions of lanthana appear to have an additional catalyst promotional effect without interfering with the chromia thermal stabilization. The increased WGS reaction rates at higher temperatures could allow for greater throughput of reactants in industrial settings. Higher concentrations of lanthana decrease the activity due to what is believed to be disruption of the chromia stabilizing effect as well as reduced amount of the active phase of catalyst. In-situ UV-Visible analysis shows that the oxidation state of the iron in the catalyst has a direct correlation to the UV-Visible light absorbance of the surface of the iron catalyst. Extent of reduction is traditionally measured with a synchrotron which is significantly more expensive than UV-Vis spectroscopy. This study uses the more economical UV-Vis spectrometer to determine similar information. The lanthana doped catalysts show an over-reduction of iron during WGS conditions (i.e. rapid reduction of Fe2O3 to Fe3O4 and FeO).
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Hallac, Basseem Bishara. "Kinetic Experimental and Modeling Studies on Iron-Based Catalysts Promoted with Lanthana for the High-Temperature Water-Gas Shift Reaction Characterized with Operando UV-Visible Spectroscopy and for the Fischer-Tropsch Synthesis." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4271.
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The structural and functional roles of lanthana in unsupported iron-based catalysts for the high-temperature water-gas shift reaction and Fischer-Tropsch synthesis were investigated. The performance of the catalysts with varying lanthana contents was based on their activity, selectivity, and stability. With regard to the former reaction, extent of reduction of the iron in Fe2O3/Cr2O3/CuO/La2O3 water-gas shift catalysts is a key parameter that was characterized using UV-visible spectroscopy. Minor addition of lanthana (<0.5 wt%) produces more active and stable catalysts apparently because it stabilizes the iron-chromium spinel, increases the surface area of the reduced catalysts, enhances the reduction of hematite to the magnetite active phase, and facilitates the adsorption of CO on the surface of the catalyst modeled by an adsorptive Langmuir-Hinshelwood mechanism. Statistical 95% confidence contour plots of the adsorption equilibrium constants show that water adsorbs more strongly than CO, which inhibits the reaction rate. A calibration curve that correlates the oxidation state of surface iron domains to normalized absorbance of visible light was successfully generated and applied to the water-gas shift catalysts. UV-visible studies indicated higher extent of reduction for surface Fe domains for the catalysts promoted with 1 wt% of lanthana and showed potential to be a more convenient technique for surface chemistry studies than X-ray absorption near edge spectroscopy (XANES). Lanthana addition to iron-based Fischer-Tropsch catalysts enhances the olefin-to-paraffin ratio, but decreases their activity, stability, and selectivity to liquid hydrocarbons. Adding lanthana at the expense of potassium reduces the water-gas shift selectivity and enhances the activity and stability of the catalysts. Finally, a model that simulates heat and mass transfer limitations on the particle scale for the Fischer-Tropsch reaction applicable at lab-scale suggests optimal operating and design conditions of 256°C, 30 bar, and 80 mirons are recommended for higher selectivity to liquid hydrocarbons. The model considers pressure drop, deactivation, pore diffusion, film heat transfer, and internal heat transfer when solving for the optimal conditions, and maps them as functions of design variables. This model can be up-scaled to provide guidance for optimal design of commercial-size reactors.
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Cordeiro, Guilherme Luís. "Estudo de síntese de catalisadores de níquel suportados em alumina-lantânia para aplicação na produção de hidrogênio a partir da reforma a vapor do etanol." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-23032015-143913/.
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O uso do hidrogênio, como vetor energético, representa uma opção promissora a fim de se reduzir a dependência dos combustíveis fósseis e controlar a emissão de poluentes na atmosfera. Atualmente, uma das rotas mais propícias para produção de hidrogênio envolve a reação de reforma a vapor de álcoois utilizando-se catalisadores de níquel suportados em alumina. O níquel é amplamente utilizado em catálise devido ao baixo custo e à elevada atividade para ruptura da ligação C-C. A alumina, por sua vez, promove maior dispersão do metal ativo devido aos valores elevados de área superficial das estruturas cristalinas de transição, sobretudo da fase gama, característica esta diretamente relacionada às condições de síntese. A incorporação de lantânia, como aditivo, tem sido considerada por moderar a acidez da superfície do suporte e minimizar a deposição de carbono no catalisador durante a reação de reforma. Tendo em vista que a atividade dos catalisadores na reação de reforma é função das características físicas e químicas desses materiais, avaliou-se, no presente trabalho, a rota de síntese por coprecipitação de hidróxidos em associação ao uso de surfactante e tratamento solvotérmico. A rota de mistura de pós de óxido de níquel com alumina, ambos preparados por precipitação individual, foi adotada para comparação dos resultados obtidos por coprecipitação. Nas condições otimizadas do processo, estudou-se o efeito da adição de óxido de lantânio nas propriedades dos materiais sintetizados. Verificou-se que o método de coprecipitação permitiu a obtenção de óxidos mistos com elevada área superficial (na faixa de 170 a 260 m2g-1), ao passo que a mistura de óxidos conduziu à formação de pós constituídos por fases distintas de alumina e óxido de níquel, com menor área superficial (na faixa de 60 a 180 m2.g-1). Após avaliação do comportamento de redução do óxido de níquel contido nesses materiais, as propriedades dos pós obtidos foram correlacionadas com o desempenho na produção de hidrogênio pela reforma do etanol. De acordo com os resultados, o catalisador preparado por coprecipitação apresentou menor atividade na produção de hidrogênio, comparativamente aos materiais obtidos por coprecipitação em associação com tratamento solvotérmico e mistura de óxidos. Em contraste, verificou-se uma menor quantidade de carbono acumulado sobre o catalisador preparado por coprecipitação, indicativo da elevada estabilidade catalítica deste material durante a reação de reforma.Hydrogen use as an energy vector represents a promising option in order to reduce the dependence on fossil fuels and to control the emission of pollutants into the atmosphere. Nowadays, one of the most important routes for hydrogen production includes steam reforming reactions of alcohols over alumina-supported nickel catalysts. Nickel is largely applied in catalysis because of its low cost and high activity for C-C bond rupture. Alumina, in turn, promotes appropriate dispersion of the active metal due to the high surface area values of its transition crystalline structures, especially gamma phase. These characteristics are related to synthesis conditions. Incorporation of lanthana as an additive has been considered to control alumina surface acidity and to inhibit catalyst deactivation by carbon deposition during reforming reaction. Considering that catalyst activity is a function of materials physical and chemical properties, it was evaluated in this work powder synthesis route by coprecipitation in association with surfactant templating method and solvothermal treatment. Mechanical milling of nickel oxide and alumina powders, which were individually prepared by chemical precipitation, was adopted for comparison purposes. Under optimized preparation conditions, the effect of lanthanum oxide addition on the materials properties was studied. It was verified that coprecipitation allowed the production of high surface area mixed oxides (170-260 m2g-1). Mechanical mixture led to the formation of materials constituted by alumina and nickel oxide phases, with low surface area (60-180 m2.g-1). After evaluation of nickel oxide reduction behavior, in hydrogen atmosphere, a correlation between properties and performance in hydrogen production by ethanol steam reforming was established. According to the results, the catalyst prepared by coprecipitation was less active for hydrogen generation compared to the ones obtained by coprecipitation followed by solvothermal treatment and mechanical milling methods. In contrast, the lowest amount of carbon deposits was found on the catalyst prepared by coprecipitation, which is an indicative of the high catalytic stability during reforming reaction.
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Boujamaa, Rachid. "Caractérisations physico-chimiques et électriques d’empilements de couches d’oxyde à forte permittivité (high-k) / grille métallique pour l’ajustement du travail effectif de la grille : application aux nouvelles générations de transistors." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENT100.
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Cette thèse s'inscrit dans le cadre du développement des technologies CMOS 32/28nm chez STMicroelectronics. Elle porte sur l'étude d'empilements de grille métal/diélectrique high-k élaborés selon une stratégie d'intégration Gate First, où le couple TiN/HfSiON est introduit avec une couche interfaciale SiON et une encapsulation de la grille TiN par du polysilicium. Cette étude s'est principalement focalisée sur l'analyse des interactions entre les différentes couches constituant les empilements, en particulier des additifs lanthane et aluminium, employés pour moduler la tension de seuil Vth des transistors NMOS et PMOS respectivement. Les analyses physico-chimiques réalisées au cours de ces travaux ont permis de mettre en évidence la diffusion en profondeur des éléments La et Al à travers le diélectrique de grille HfSiON sous l'effet du recuit d'activation des dopants à 1065°C. Les résultats obtenus ont montré que ce processus de diffusion entraine une réaction du lanthane et de l'aluminium avec la couche interfaciale de SiON pour former un silicate stable La(ou Al)SiO au profit de la couche de SiON. L'analyse des propriétés électrique des structures MOS a permis de révéler que la présence d'atomes La ou Al proximité de l'interface HfSiON/SiON conduit à la présence d'un dipôle généré à cette interface, qui a pour effet de décaler le travail de sortie effectif de la grille métalliqueThis thesis is part of the development of CMOS technologies 32/28nm STMicroelectronics. It focuses on the study of stacks of metal / high-k dielectric prepared by an integration strategy Gate First , where the couple TiN / HfSiON gate is introduced with an interfacial layer SiON and encapsulation of TiN gate polysilicon by . The study was mainly focused on the analysis of interactions between the various layers forming the stacks , in particular lanthanum and aluminum additives , used for modulating the threshold voltage Vth of the PMOS and NMOS transistors respectively . The physico-chemical analyzes in this work helped to highlight the depth distribution of the elements La and Al through the HfSiON gate dielectric under the influence of dopant activation annealing at 1065 ° C. The results obtained showed that this diffusion process causes a reaction of lanthanum and aluminum with the interfacial layer of SiON to form a stable silicate La ( or Al ) SiO benefit of the SiON layer . The analysis of electrical properties of MOS structures revealed that the presence of the atoms near the Al or HfSiON / SiON interface leads to the presence of a dipole generated at this interface , which has the effect of shifting actual output work of the metal gate
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Dahdah, Eliane. "The role of Mg-Al hydrotalcite derived mixed oxides as catalytic support materials : Applications in the transesterification of vegetable oils for biodiesel production and in the steam reforming of glycerol for hydrogen production." Thesis, Littoral, 2018. http://www.theses.fr/2018DUNK0498/document.
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Ce travail vise à étudier la transestérification de l'huile de tournesol pour la production de biodiesel et le vaporeformage du glycérol pour la production d'hydrogène renouvelable. Les oxydes mixtes Mg-Al prépares par voie hydrotalcite ont été choisis comme supports catalytiques. Pour la production de biodiesel, les effets du traitement thermique et de la méthode de préparation pour l'incorporation de calcium ont été étudiés. Le catalyseur Ca600/Mg₄Al₂HT calciné à 600°C, préparé par imprégnation de 40 wt% de Ca sur le support Mg₄Al₂ non calciné, a montré les meilleures performances catalytiques en raison de ses propriétés basiques améliorées. Pour le vaporeformage catalytique du glycérol, l'activité des oxydes de métaux purs imprégnés par le Ni a d'abord été étudiée, puisque les oxydes de métaux purs sont souvent utilisés comme supports catalytiques. Le catalyseur Ni/ZrO₂ s'est révélé le plus efficace pour la production d'hydrogène. Pour le vaporeformage du glycérol en présence d'oxydes mixtes obtenus par voie hydrotalcite, les catalyseurs au Ru-Mg-Al ont été étudiés. L'effet de la méthode de préparation (imprégnation ou greffage) sur l'activité catalytique a été étudié. Le catalyseur préparé par imprégnation permettait une plus grande accessibilité à la phase active. Pour des catalyseurs Ni-Mg-Al, les supports ont été modifiés par du lanthane. Le catalyseur Ni/Mg₆Al₁.₆La₀.₄ était le plus performant en raison de sa basicité accrue et de son interaction métal-support. Les activités des catalyseurs Ni/ZrO₂ et Ni/Mg₆Al₁.₆La₀.₄ ont été comparées. Les deux catalyseurs ont produit des rendements en hydrogène similaires. Moins de coke a été produit sur le catalyseur préparé par voie hydrotalcite, en raison de sa basicité supérieure. Un test de stabilité à 600°C a montré la désactivation du catalyseur Ni/Mg₆Al₁.₆La₀.₄ après 6 heures. Lors de l'optimisation des conditions de réaction sur le catalyseur Ni/Mg₆Al₁.₆La₀.₄, une amélioration significative de la stabilité a été observée, étendant ainsi sa durée de vie à 24 heuresThis work aims to study the transesterification of sunflower oil for biodesel production and the steam reforming of glycerol for renewable hydrogen production. Mg-Al hydrotalcite derived mixed oxides were chosen as catalytic support materials given their known basicity, thermal stability and low cost. Only one active phase was studied for biodiesel production (Ca) and two different active phases (Ru and Ni) for glycerol steam reforming. The various prepared catalysts were characterized by different techniques such as X-Ray Diffraction (XRD), specific surface area determination by BET method, Fourier Transform Infrared Spectroscopy (FTIR), H₂-Temperature Programmed Reduction (H₂-TPR), CO₂-Temperature Programmed Desorption (CO₂-TPD) and Simultaneous Thermogravimetric-Differential Scanning Calorimetry (TG-DSC). For biodiesel production, the effects of thermal treatment and the preparation method for Ca incorporation were both studied. The catalyst that showed the best catalytic performance was an uncalcined Mg₄Al₂ support impregnated with 40 wt% Ca followed by a calcination at 600°C (Ca/600Mg₄Al₂HT) due to its enhanced basic properties. After several optimization steps over this catalyst, the optimum conditions for biodiesel synthesis were: a methanol to oil molar ratio of 15:1, a catalyst to oil ratio of 2.5 wt% and a reaction time of 6 hours which gave a FAME yield of 95%. The properties of the produced biodiesel were studied and found to be in good agreement with ASTM (American Society for Testing and Materials) requirements. For the catalytic steam reforming of glycerol, the activity of NI-based pure metal oxides (Ni/CeO₂, Ni/Y₂O₃, Ni/ZrO₂) was first studied as pure metal oxides are commonly used as support materials. The effect of the support was evaluated and the Ni/ZrO₂ catalyst was found to be the most efficient for hydrogen production. To study the effect of the zirconia phase, a tetragonal Ni/ZrO₂ was also prepared. The tetragonal catalyst was less active for hydrogen production compared to the monoclinic catalyst. A stability test at 600°C also showed the desactivation of the tetragonal Ni/ZrO₂ after 6 hours on stream. For the catalytic steam reforming of glycerol using Mg-Al hydrotalcite derived mixed oxides, Ru-based Mg-Al catalysts were first studied. The effect of the preparation method (impregnation vs grafting) on the catalytic activity of Ru-Mg-Al catalysts was studied. The catalyst prepared by the impregnation method resulted in a better catalytic activity than the catalyst prepared by the grafting method as it allowed a higher accessibility of the active phase. For the Ni-based Mg-Al catalysts, the hydrotalcite supports were modified with La to study the effects of promoter addition on catalytic properties and activity. The bimetallic effect (1%Ru-5%Ni) and effect of a higher Ni loading (15 wt%) were also studied. The 5 wt% Ni impregnated on a La modified Mg-Al support (Ni/Mg₆Al₁.₆La₀.₄) catalyst was the most efficient for hydrogen production due to its enhanced basicity and metal-support interaction. The activities of the most efficient catalysts, Ni/ZrO₂ and Ni/Mg₆Al₁.₆La₀.₄, were compared. Both catalysts produced similar hydrogen yields. Differences in glycerol conversion to gaseous products were attributed to a higher formation of liquid by-products over the hydrotalcite support compared to the zirconia support. Nevertheless, less coke was produced over the hydrotalcite catalyst given its higher basicity. A stability test at 600°C showed the desactivation of the Ni/Mg₆Al₁.₆La₀.₄ catalyst after 6 hours on stream. Upon optimization of the reaction conditions on Ni/Mg₆Al₁.₆La₀.₄, a significant improvement in the stability was observed as the catalyst lasted for 24 hours on steam.Therefore, Ni/Mg₆Al₁.₆La₀.₄ could be a promising candidate for industrial application
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Abou, Rached Jihane. "Production d'hydrogène par reformage catalytique du toluène sur des oxydes mixtes Ni-Mg-Al : Effet de l'ajout de cérium ou de lanthane." Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0442/document.
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Cette thèse a été réalisée dans le cadre de la valorisation des composés organiques volatils (COVs) tels que le toluène. Cette étude vise à mettre au point des catalyseurs efficaces pour l'élimination du toluène par reformage à sec et vaporeformage du toluène. Les solides de type hydrotalcite ont été choisis en raison des propriétés intéressantes des oxydes obtenus par leur calcination. Les catalyseurs à base de Ni, Mg, et Al ont été préparés par voie hydrotalcite. Afin d'améliorer l'activité catalytique, les éléments Ce et La ont été incorporés dans les solides pour substituer une partie de l'élément Al et les effets ont été étudiés. Dans un premier temps, les différents oxydes mixtes ont été caractérisés par différentes techniques physico-chimiques dont la Diffraction des Rayons X (DRX), les Analyses Thermiques (ATD, ATG), la Réduction en Température Programmée (RTP),... Dans un deuxième temps, les différents oxydes mixtes ainsi préparés ont été testés dans les réactions de reformage à sec du toluène. La substitution progressive des ions Mg²⁺ par les ions Ni²⁺ améliore l'activité des catalyseurs. Le cérium ou le lanthane interviennent au niveau du mécanisme réactionnel pour améliorer la sélectivité tout en réduisant le dépôt de carbone. Les performances catalytiques des oxydes sont ensuite testées vis-à-vis de la réaction de vaporeformage du toluène montrant que la réactivité s'améliore avec l'augmentation de la teneur en magnésium. Les promoteurs ont montré un effet sur la conversion et la sélectivité en hydrogène. Selon les caractérisations physico-chimique après test catalytique, les catalyseurs n'ont montré aucune formation de coke. Une comparaison entre le meilleur catalyseur de cette étude et un catalyseur industriel est abordéeThis thesis was carried out in the context of the valorization of volatile organic compounds (VOCs) such as toluene. This study aimed to optimize efficient catalysts for the elimination of toluene by dry and steam reforming of toluene. Hydrotalcite solids were chosen because of the interesting properties of the oxides obtained by their calcination. The Ni, Mg and Al-based catalysts were prepared via hydrotalcite road. In order to improve the catalytic activity, the elements Ce and La were incorporated into the solids to substitute a part of the element A1 and the effects were studied. Initially, the mixed oxides were characterized by different physico-chemical techniques including X-Ray Diffraction, Thermal Analysis (TG/DTA), Temperature Programmed Reduction (TPR),... In a second step, the mixed oxides were tested in the dry reforming of toluene reaction. The progressive substitution of Mg²⁺ ions by Ni²⁺ ions improves the activity of the catalysts. Cerium or lanthanum played a role in the reaction mechanism, to improve selectivity and reduce carbon deposition. The catalytic performances of the oxydes are tested in the steam reforming of toluene reaction, showing that the reactivity improves with the increase in the magnesium content. The promoters have enhanced the toluene conversion and hydrogen selectivity. According to the physico-chemical characterizations after the catalytic test, the catalysts showed no coke formation. A comparison between the best catalyst of this study and an industrial catalyst is performed
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Vilasi, Pauline. "Synthèse de nouveaux catalyseurs nanostructurés par dépôts physiques à base de pérovskite de lanthane." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCA041.
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Ce travail de thèse est issu d’une collaboration entre les laboratoires de recherche FEMTO-ST de l’université technologique de Belfort-Montbéliard et IRCELYON de l’université Claude Bernard à Villeurbanne. Les objectifs de cette étude portent sur la faisabilité d’élaborer par pulvérisation cathodique magnétron des films minces de cobaltite de lanthane nanostructurés. En effet, ces films présentent des propriétés catalytiques intéressantes pour l’oxydation des composés organiques volatiles comme le propène (C3H6) ou le monoxyde de carbone (CO) qui constituent la principale source de pollution de l’air. Il sera montré dans un premier temps que les cobaltites de lanthane de formule LaCoO3 ne sont pas efficaces pour ce type d’application. La composition chimique de ce matériau sera donc modifiée en y incorporant de l’argent de manière à faire varier les propriétés physico-chimiques des films et d’augmenter leurs performances catalytiques. La morphologie des films est directement impactée par l’introduction de Ag puisqu’elle évolue d’un système dense à un système « nanofilaire ». Une autre série de dépôts sera également élaborée et testée en catalyse constituée de cobaltites de lanthane dopées avec de l’argent mais aussi du cérium. On retiendra alors que les films de LaCoO3 + Ag sont plutôt efficaces et prometteurs puisqu’ils présentent des performances catalytiques se rapprochant de celles du platine (catalyseur de référence). Néanmoins, bien que les films aient toujours cette morphologie nanofilaire, les compositions chimiques des films élaborés à base de LaCoO3 + Ag + Ce doivent être optimisées afin d’augmenter leurs activités catalytiquesThis work was made in the frame of a scientific research relationships between the laboratory FEMTO-ST of the Technological University of Belfort-Montbéliard and the laboratory IRCELYON of the Claude Bernard University of Villeurbanne. This study aims at characterizing the feasibility of nanostructured lanthanum cobaltite thin films via magnetron sputtering. Indeed, it is well known these materials have interesting catalytic properties regarding the oxidation of volatile organic compounds such as propene (C3H6) or carbon monoxide (CO), the latter being the main source of air pollution. First, it has been shown that lanthanum cobaltites of formula LaCoO3 are not efficient for this type of application. The chemical composition of this material was then modified by incorporating silver so as to vary the physicochemical properties of the films and increase their catalytic performance. In consequence, the morphology of the films was directly impacted by the introduction of Ag since it evolved from a dense system to a "nanowire" system. Another series of deposits based on cobaltite modified by both silver and cerium additions have been also developed and tested during catalytic tests. It should be noted that the Ag containing thin films of LaCoO3 are rather efficient and then promising since they have catalytic performances close to those of platinum (the reference catalyst). Concerning the Ag and Ce containing perovskite films, although they still have this peculiar nanowired morphology, their chemical compositions have to be optimized in order to increase their catalytic activities
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Regny, Sylvain. "Nanocristaux multifonctionnels pour l'élaboration de sondes biologiques." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI056.
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La médecine s’intéresse de plus en plus à des systèmes nanométriques visant la détection précoce de cellules malignes, le traitement de ces dernières ou la compréhension de mécanismes biologiques. Des nanoparticules fluorescentes et des nanocristaux harmoniques aux propriétés non-linéaires intéressantes ont été étudiés comme agents de contraste pour l’imagerie biomédicale.Dans ce travail, nous avons recherché un matériau non-centrosymétrique dont la matrice permet un dopage d’ions lanthanides afin de développer des sondes multifonctionnelles, c’est-à-dire à la fois luminescentes et harmoniques. Nous nous sommes orientés vers l’iodate de lanthane de phase alpha, α-La(IO3)3, non-centrosymétrique. Dans un premier temps, nous avons développé des synthèses hydrothermales assistées par micro-ondes pour permettre de cristalliser la phase alpha et produire des particules de taille nanométrique (< 100 nm). La présence de nombreux pseudo-polymorphes nécessite le contrôle précis des paramètres de synthèse, en particulier de la température de synthèse, pour obtenir exclusivement des nanoparticules de α-La(IO3)3. L’étude de différents intermédiaires réactionnels (La(IO3)3(OH2), La(IO3)2.66(OH)0.33) nous a permis de mettre en évidence une transformation de phase entre ces composés et la phase α-La(IO3)3. Dans un deuxième temps, nous avons utilisé deux dispositifs optiques permettant de mesurer l’efficacité de génération de second harmonique : l’un permettant l’étude de nanocristaux de α-La(IO3)3 individuels et l’autre utilisant un ensemble de nanocristaux en suspension dans un solvant. Ce dernier, basé sur la diffusion Hyper-Rayleigh, nous a permis de quantifier la réponse non-linéaire de nanocristaux α-La(IO3)3 de diamètre 20-50 nm et de déterminer un coefficient non-linéaire < d > de 8 pm.V-1, comparable aux valeurs obtenues pour d’autres nanocristaux harmoniques tels que BaTiO3 ou LiNbO3. Enfin, nous avons montré la possibilité d’incorporer des ions lanthanides tels que Er3+ et Yb3+ dans ces nanocristaux d’iodate de lanthane, conduisant à des nanocristaux de α-La1-x-yYbyErx(IO3)3. Ces nanocristaux sont toujours actifs en génération de second harmonique et émettent simultanément un signal de photoluminescence. Ainsi, pour une excitation dans le proche infra-rouge (800 nm ou 980 nm par exemple), nous avons observé simultanément un signal de second harmonique et de photoluminescence par up-conversion. Nous avons démontré l’intérêt d’un co-dopage Yb3+/Er3+ pour une optimisation du signal d’up-conversion sous une excitation à 980 nm. Ainsi, par un dopage d’ions lanthanides tels que Er3+ et Yb3+, les nanocristaux de α-La(IO3)3 présentent une émission simultanée de génération de second harmonique et de photoluminescence. La combinaison de ces deux propriétés permet d’envisager d’utiliser ces nanocristaux bifonctionnels pour une imagerie par luminescence, technique classique, tout en la couplant avec une imagerie multiphoton, plus coûteuse mais présentant des avantages non-négligeables (rapidité de scans, meilleure sélectivité spatiale, sensibilité à la polarisation)Medicine is increasingly interested in nanometric systems for the early detection of malignant cells, their treatment or understanding of biological mechanisms. Fluorescent nanoparticles and harmonic nanocrystals with interesting non-linear properties have been studied as contrast agents for biomedical imaging.In this work, we explored a non-centrosymmetric material whose matrix allows a doping of lanthanide ions in order to develop multifunctional probes, i. e. both luminescent and harmonic. We focused on non-centrosymmetric iodate phase: alpha lanthanum iodate, α-La(IO3)3. First, we developed microwave-assisted hydrothermal syntheses to crystallize the alpha phase and produce nano-sized particles (< 100 nm). The presence of many pseudo-polymorphs requires precise control of the synthesis parameters, in particular the synthesis temperature, to obtain exclusively nanoparticles of α-La(IO3)3. The study of different reaction intermediates (La(IO3)3(OH2), La(IO3)2.66(OH)0.33) allowed us to identify a phase transformation between these compounds and the phase α-La(IO3)3. Secondly, we used two optical devices to evaluate the second harmonic generation efficiency of the synthesized α-La(IO3)3 nanocrystals: one set-up allowed us to study individual α-La(IO3)3 nanocrystals and the other used an ensemble of α-La(IO3)3 nanocrystals in suspension in a solvent. The latter, based on Hyper-Rayleigh scattering, quantified the non-linear response of nanocrystals α-La(IO3)3 with a diameter of 20-50 nm and allowed us to determine a non-linear coefficient < d > of 8 pm.V-1, a value comparable to the ones obtained for other harmonic nanocrystals such as BaTiO3 or LiNbO3. Finally, we showed the possibility of incorporating lanthanide ions such as Er3+ and Yb3+ into these lanthanum iodate nanocrystals, leading to α-La1-x-yYbyErx(IO3)3 nanocrystals. These nanocrystals are still active in second harmonic generation and simultaneously emit a photoluminescence signal. Thus, for excitation in the near infrared (800 nm or 980 nm for instance), we simultaneously observed a signal of second harmonic and a photoluminescence signal based on up-conversion processes. We demonstrated the interest of an Yb3+/Er3+ co-doping for an optimization of the up-conversion signal under excitation at 980 nm. Thus, Er3+ and Yb3+-doped nanocrystals of α-La(IO3)3 exhibit simultaneous emission of second harmonic generation and photoluminescence. The combination of these two properties makes it possible to consider using these bifunctional nanocrystals for conventional luminescence imaging, while coupling it with multiphoton imaging, which is more expensive but has significant advantages (scan speed, better spatial selectivity, polarization sensitivity)
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Baudot, Sylvain. "Elaboration et caractérisation des grilles métalliques pour les technologiesCMOS 32 / 28 nm à base de diélectrique haute permittivité." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENT122/document.
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Cette thèse porte sur l'élaboration et la caractérisation des grilles métalliques en TiN, aluminium et lanthane pour les technologies CMOS gate-first à base d'oxyde high-k HfSiON. L'effet de l'épaisseur et de la composition des dépôts métalliques a été caractérisé sur les paramètres de la technologie 32/28nm. Ces résultats ont été reliés à une variation de travail de sortie au vide du TiN, à des dipôles induits par l'Al et le La à l'interface HfSiON/SiON et à leur diminution aux petites épaisseurs de SiON (roll-off). Nous avons montré que l'aluminium déposé sous forme métallique dans le TiN cause une diminution de son travail de sortie, opposée au faible dipôle positif induit par l'Al. Nous avons évalué l'influence du roll-off pour ces différents métaux et mis en évidence pour la première fois sa forte dépendance avec l'épaisseur de lanthane déposée. Le développement de procédés de dépôt de TiN, Al, La a permis d'accroître les bénéfices de ces matériaux pour la technologie CMOS 32/28nmThis thesis is about the manufacturing and the characterization of TiN, aluminum and lanthanum metal gate for high-k based 32/28nm CMOS technologies. The effect of metal gate layer thickness and composition has been characterized on 32/28nm technology parameters. These results have been related to a change in the TiN vacuum work function, to Al- and La- induced dipoles at the HfSiON/SiON interface or their lowering on thin SiON (roll-off). We have shown that metallic aluminum introduced in the TiN metal gate causes a work function lowering, opposed to the weak Al-induced dipole. We have evaluated the roll-off influence for theses different metals. For the first time we report the strong roll-off dependence with the deposited lanthanum thickness. Newly developed TiN, Al, La deposition processes have brought benefits for the CMOS 32/28nm technology
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Abram, Edward John. "Synthesis and characterisation of doped lanthanum gallate and lanthanum silicate oxide-ion conductors." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251374.
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Li, Shuai. "Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides." Doctoral thesis, Stockholm : Skolan för industriell teknik och management, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10588.
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Hofmann, Dirk. "Messung der paritätsverletzenden Neutronenspin-Rotation in 139La unter Einsatz von 3He-Neutronenspin-Filtern." [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2000/0127/diss.pdf.
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Hübinger, Frank. "Elektronische Struktur im Volumen und an der Oberfläche von Lanthanidmaterialen eine Röntgenemissions- und inverse Photoemissionsstudie /." [S.l. : s.n.], 1999. http://www.diss.fu-berlin.de/2000/49/index.html.
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Berenov, Andrey Valdimirovich. "Cation deficiency in lanthanum manganites." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322303.
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Basiouny, Miriam M. I. "Lanthanum Catalyzed Hydrophosphination and Hydrophosphinylation." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1525441044040006.
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Boyaval, Jérôme. "Synthèses et propriétés optiques de complexes lanthanidiques d'alcanoates de cholestéryle." Artois, 2000. http://www.theses.fr/2000ARTO0402.
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L'objectif de ce travail était de réaliser des matériaux alliant les avantages pour l'optique de la structure torse des cristaux liquides cholestériques et les propriétés émissives des ions de terres rares. Les applications de tels milieux dits actifs sont très nombreuses. Il peuvent entre autres être utilisés pour l'élaboration de laser à rétroaction distribuée, de filtres ou de polariseurs actifs, etc pour concevoir ces matériaux photoluminescents, il a fallu synthétiser des complexes de lanthanides possédant une bonne luminescence et capables de s'insérer de manière homogène dans un cristal liquide cholestérique sans en endommager le caractère mésomorphe. L'étude spectroscopique de ces composés a été effectuée, pour pouvoir évaluer leur capacité à être pompés efficacement par un laser argon, leur potentiel de fluorescence et éventuellement leur utilisation en tant que dopants dans un milieu amplificateur. Lors de cette étude, un grand nombre de paramètres optiques tels que les paramètres d'intensité Judd-Ofelt, les probabilités de transition radiatives, les durées de vie radiatives et de fluorescence des niveaux émetteurs, les rapports de branchement, les sections efficaces d'émission et les rendements quantiques ont été estimés. A l'issue de cette analyse, une étude des processus de transfert d'énergie entre le métal et les ligands a été effectuée. A l'aide de la théorie du champ de ligand le degré d'hydratation des complexes de lanthanides a pu être déterminé. Enfin, l'étude de la propagation de la lumière émise par un dopant, au sein même d'un cristal liquide cholestérique senestre, pour des longueurs d'onde situées dans et en dehors de la bande de réflexion sélective a été entreprise.
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Risterucci, Paul. "Coupling of electron spectroscopies for high resolution elemental depth distribution profiles in complex architectures of functional materials." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0047/document.
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Ce travail de thèse est focalisé sur la détermination, de manière non-destructive, d'interfaces profondément enterrées dans des empilements multi-couches utilisés dans les conditions de technologie réelles au travers d'une méthode innovante basée sur la photoémission avec utilisation de rayons-x de haute énergie (HAXPES) et l'analyse du fond continu inélastique. Au cours de cette thèse, une procédure numérique a été développée pour quantifier la correspondance entre la mesure du fond continu faite par HAXPES et la simulation du fond continu représentative d'une distribution en profondeur donnée. Cette méthode permet de trouver la distribution en profondeur d'un élément grâce à une procédure semi automatisée. Dans un premier temps cette méthode a été testée en étudiant une couche ultra fine de lanthane enterrée à une profondeur >50 nm dans un dispositif de grille métallique high-k. L'influence des paramètres utilisés lors de l'analyse y est étudiée et révèle l'importance principale d'un paramètre en particulier, la section efficace de diffusion inélastique. La combinaison de mesures HAXPES avec l'analyse du fond continu inélastique utilisant cette nouvelle méthode permet d'augmenter la profondeur de sonde jusqu'à un niveau sans précédent. Ainsi l'échantillon peut être sondé jusqu'à 65 nm sous la surface avec une haute sensibilité à une couche nanométrique. Dans un second temps, la méthode précédemment validée d'analyse de fond continu inélastique est combinée avec une étude haute résolution des niveaux de cœur dans un échantillon servant de source dans un transistor à haute mobilité. Les deux analyses sont complémentaires puisqu'elles permettent d'obtenir la distribution en profondeur des éléments ainsi que leur environnement chimique. Le résultat donne une description complète des diffusions élémentaires dans l'échantillon suivant les différentes conditions de recuitThis thesis tackles the challenge of probing in a non-destructive way deeply buried interfaces in multilayer stacks used in technologically-relevant devices with an innovative photoemission method based on Hard X-ray PhotoElectron Spectroscopy (HAXPES) and inelastic background analysis. In this thesis, a numerical procedure has been implemented to quantify the matching between a HAXPES measured inelastic background and a simulated inelastic background that is representative of a given depth distribution of the chemical elements. The method allows retrieving depth distributions at large depths via a semi-automated procedure. First, this method has been tested by studying an ultra-thin layer of lanthanum buried at depth >50 nm in a high-k metal gate sample. The influence of the parameters involved in the analysis is studied unraveling the primary importance of the inelastic scattering cross section. The combination of HAXPES with inelastic background analysis using this novel method maximizes the probing depth to an unprecedented level, allowing to probe the sample up to 65 nm below the surface with a high sensitivity to a nm-thick layer. Second, the previously-checked inelastic background analysis is combined with that of high resolution core-level spectra in the case of the source part of a high electron mobility transistor. The two analyses are complementary as they allow retrieving the elemental depth distribution and the chemical state, respectively. The result gives a complete picture of the elemental intermixing within the sample when it is annealed at various temperatures
Denne afhandling omhandler problemet med at probe dybt begravede grænseflader i multilags stacks, som bruges i teknologisk relevante devices, med en innovativ fotoemissions metode, der er baseret på Hard X-ray PhotoElectron Spectroscopy (HAXPES) og analyse af den uelastiske baggrund. I afhandlingen er en numerisk procedure blevet implementeret til at kvantificere forskellen mellem en HAXPES målt uelastisk baggrund og en modelleret baggrund, som svarer til en given dybdefordeling af atomerne. Metoden muliggør, med en halv-automatisk procedure, at bestemme dybdefordelingen i store dybder. Metoden er først blevet testet ved at studere et ultra-tyndt lag af lanthan, som er begravet i en dybde > 50 nm i en high-k-metal-gate prøve. Indflydelsen af parametrene der ingår i analysen er blevet studeret for at opklare den primære betydning af det anvendte uelastiske spredningstværsnit. Kombinationen af HAXPES med analyse af den uelastiske baggrund og brug af den nye numeriske metode giver en hidtil uset probe-dybde, som giver mulighed for at probe den atomare sammens ætning i op til 65 nm dybde under overfladen og med høj følsomhed af et kun nm tykt lag. Dernæst er den uelastiske baggrundsanalyse blevet kombineret med højopløst core-level spektroskopi for at studere de aktive dele i en høj-elektronmobilitets transistor. De to analyser er komplementære, idet de henholdsvis bestemmer den atomare fordeling og atomernes kemiske bindingstilstand. Resultatet giver et fuldstændigt billede af atomernes omfordeling i prøven når denne opvarmes til forskellige temperaturer
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Tranvouez, Nolwenn. "Élaboration et caractérisation de films minces de cuprate de lanthane." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0196/document.
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Le La2CuO4 est un isolant antiferromagnétique qui devient supraconducteur lorsqu'il est suffisamment oxydé. Cette étude qui porte sur la faisabilité de la synthèse de films de La2CuO4 par pulvérisation magnétron sur des substrats à moindre coût a été développée selon trois axes : l'élaboration des films, l'étude de leur cristallisation et l'influence de la nature du substrat sur leur tenue mécanique. Sous l'aspect élaboration ont été regroupés la présentation et la comparaison de quatre procédés d'élaboration. Nous avons ainsi déterminé que le procédé utilisant une cible céramique est le procédé permettant d'obtenir la zone homogène la plus étendue. La structure des films après recuit dans l'air a été déterminée par diffraction des rayons X et par microscopie électronique en transmission. Ces techniques ont permis de démontrer que les films cristallisent majoritairement dans une structure quadratique métastable et dans une moindre mesure dans une structure orthorhombique. L'effet de la composition chimique des films, de la nature du substrat et sur la cristallisation des films ont été étudiés. Il apparaît que l'utilisation de substrats en acier constitue une voie prometteuse pour la synthèse de films de La2CuO4. En utilisant des techniques de microscopie in situ, nous avons démontré que le recuit induit la formation de défauts en surface des films. La nature de ces défauts dépend des propriétés thermiques des substrats. Pour expliquer ces résultats, nous avons estimé les coefficients de dilatation thermique apparents de nos films à partir d'analyses par diffraction des rayons X. Ceci nous a permis de proposer un modèle d'initiation de la délamination des filmsLanthanum cuprate is an antiferromagnetique insulator that becomes superconducting when sufficiently oxidized. The aim of this study is to show the feasibility of the lanthanum cuprate thin film deposition by magnetron sputtering on low cost substrates. This work is developed around three points: the synthesis of the films, a study of their crystallization and the influence of the substrate nature on the films delamination. The synthesis aspect includes the presentation of the four different synthesis processes and a comparison of these processes in terms of reproducibility, chemical composition and thickness homogeneous zones. The process using a ceramic target was determined to have the larger homogeneous zone but does not allow obtaining stoichiometric films. The films structure after annealing in air has been determined by X-ray diffraction and Transmission Electronic Microscopy. This technique allowed us to demonstrate that the films mostly crystallize in a metastable tetragonal structure and in a lesser extend in orthorhombic structure. The effects of the chemical composition of the film, the substrate nature, and the annealing atmosphere on the films crystallization were studied. The use of steel as a substrate is promising way to the elaboration of La2CuO4 thin films. By using in situ microscope techniques, we showed that the thermal treatment induces defaults formation on the film surface. The natures of these defaults strongly depend on the substrate nature. To explain these results, the apparent thermal expansion coefficients of the films were calculated from x-ray diffraction analyses. These results allowed us to suggest a film delamination initiation model
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Negahdari, Zahra. "Reaction sintered alumina-lanthanum hexaaluminate composites." Aachen Shaker, 2009. http://d-nb.info/1000213897/04.
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Johnston, Diane E. "Characterisation of lanthanum-doped barium titanate." Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU554634.
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One significant application of donor doped barium titanate (BaTiO3) is in the manufacture of Positive Temperature Coefficient of Resistance (PTCR) thermistors. Combined synthesis, phase diagram and electrical studies were undertaken on donor doped barium titanate with a view to understanding the factors responsible for PTCR phenomena. A range of materials, both commercial PTCR devices and in-house lanthanum-doped barium titanate samples, have been studied. All three commercial PTCR samples measured were found to be electrically inhomogeneous with two PTCR-exhibiting regions and a conductive grain core. The conductive core resistance had a characteristic temperature dependence, with a minimum occurring in the vicinity of the tetragonal to cubic phase transition (Tc) of barium titanate. The phase relations and electrical behaviour of two joins in the lanthanum-doped BaTiO3 system, join A (Ba4-4xLa4xTi4-xO12) and join B (Ba1-yLayTiO3+), were also studied. Compositions on joins A and B for 0x0.195 and 0y0.1 respectively, crystallised as single phase barium titanate. Charge compensation on both joins (at these concentrations) was achieved by a mixture of both titanium vacancies and free electrons. The electron compensation mechanism, Ba_1-yLa_yTi. 4+_1-yTi. 3+O_3, significantly complicates determination of phase relations in this system, since it occurs off the BaO-TiO_2-La_2O_3 ternary phase diagram. Ac impedance measurements indicated that samples on join A were electrically inhomogeneous resulting in the presence of different regions with variable Tx values; furthermore, the phase transitions in each region were themselves complex. The tetragonal to cubic phase transition was studied by a combination of x-ray diffraction, ac impedance and by varying dopant concentration. The resulting behaviour was complex, with both first order and continuous transitions occurring. There was also evidence of a two phase, (i.e. both cubic and tetragonal barium titanate) region associated with a distribution in particle size: small particles (&60 2m) were cubic; larger ones were tetragonal. It is apparent that the combined, complicating effects of grain size and segregation phenomena make it inappropriate to give an explanation for the phase relations and electrical behaviour of lanthanum-doped barium titanate in terms of classical phase equilibria and phase transition theories.
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Lacombe, Sylvie. "Etude mécanistique du couplage oxydant du méthane sur oxyde de lanthane." Lyon 1, 1993. http://www.theses.fr/1993LYO10276.
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Le mecanisme du couplage oxydant du methane a ete etudie sur un oxyde de lanthane (caracterise par xps, ftir, xrd, tem, sem) en utilisant les techniques de cinetique rapide avec marquage isotopique sur reacteur dynamique (equilibre ch#4/cd#4, transitoires a l'etat stationnaire) et la technique pulsee sur reacteur tap. Le schema mecanistique suivant a ete propose. Le methane gazeux s'active soit reversiblement et heterolytiquement sur des sites acido-basiques la#3#+-o#2#, soit irreversiblement et homolytiquement sur des sites fortement basiques de type o# pour former un radical methyle. Les sites o# sont issus de l'activation dissociative de l'oxygene sur une paire (o#2#, lacune anionique). La grande mobilite de l'oxygene de reseau fait que ces sites ne sont pas localises. Le couplage des radicaux methyles en ethane s'opere en phase gaz et l'ethane peut etre deshydrogene par la suite en ethylene. L'origine du monoxyde de carbone est probablement liee a une oxydation en phase gaz des hydrocarbures. Le dioxyde de carbone provient de l'oxydation des radicaux methyles par une succession d'etapes de surface, faisant intervenir des groupements methoxy puis carbonates. Les sites impliques seraient des sites faiblement coordines, localises sur les defauts de structure des particules. Ce schema mecanistique a permis d'elaborer un schema cinetique general de la reaction, avec modelisation des equations cinetiques et optimisation des principaux parametres
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LE, VAN TIEP. "Couplage oxydant du methane sur catalyseurs a base d'oxyde de lanthane." Paris 6, 1992. http://www.theses.fr/1992PA066231.
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La reaction de couplage oxydant du methane a ete etudiee en mode simultane, sur oxyde de lanthane prepare dans les conditions controlees, dans le domaine de temperature compris entre 650 et 950c. Oxyde de lanthane et oxyde de samarium possedent une bonne productivite en produits de couplage et sont stables aux temperatures elevees de la reaction. La selectivite en produits de couplage de l'oxyde de lanthane est remarquablement eleve. La reaction de com sur oxyde de lanthane est sensible a la morphologie au sens ou la selectivite en produits de couplage varie en fonction de morphologie des particules d'oxyde. La selectivite en produits de couplage diminue avec la conversion et a isoconversion du methane la selectivite et le rendement en produits de couplage passent par un maximum situe entre 850-900c. Les etudes de formation et de stabilite de l'oxycarbonate de lanthane indiquent qu'il est possible d'ameliorer les performances catalytiques des catalyseurs a base d'oxyde de lanthane par des traitements chimiques in situ. Une partie du dioxyde de carbone forme dans la reaction de com provient de l'oxydation du methane a la surface de l'oxyde de lanthane via la formation et la decomposition de l'oxycarbonate. Le dopage de l'oxyde de lanthane par du strontium apporte une amelioration de selectivite en produits de couplage pour les catalyseurs prepares a haute temperature (800c )
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Sellès, Olivier. "Halogénures de lanthane dopés cérium : des scintillateurs rapides pour l'imagerie médicale." Paris 6, 2006. https://pastel.archives-ouvertes.fr/tel-00135649.
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Ce travail concerne l’étude de cristaux scintillateurs inorganiques découverts récemment : LaCl3:Ce3+ et LaBr3:Ce3+, caractérisés par une réponse rapide, un rendement lumineux élevé et une excellente résolution énergétique, et particulièrement intéressants pour l’imagerie médicale. La forte hygroscopie de ces matériaux nécessite l’adaptation des modes opératoires habituels pour la détermination des caractéristiques physico-chimiques. . La bonne compréhension du mécanisme de scintillation et de l’effet des défauts présents dans le matériau permet d’envisager des pistes pour l’optimisation des performances du scintillateur. Dans ce sens, plusieurs techniques sont utilisées (RPE, radioluminescence, excitation laser, thermoluminescence,. . . ). La connaissance des divers processus impliqués dans le mécanisme de scintillation conduit à prévoir l’effet de la température et du taux de dopage sur les performances du scintillateur.
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Boulenc, Pierre. "Étude théorique d'interfaces pour l'épitaxie de l'aluminate de lanthane sur silicium." Lille 1, 2007. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2007/50376-2007-Boulenc.pdf.
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La miniaturisation des dispositifs Métal-oxyde-Semiconducteur (MOS) nécessitera pour l'industrie microélectronique de disposer à brève échéance d'un isolant de grille remplaçant SiO2 dont la trop faible épaisseur ne permettra plus d'assurer des performances suffisantes. La solution envisagée consiste à utiliser une couche plus épaisse d'un matériau de constante diélectrique supérieure (high-K). Afin de s'affranchir des défauts inhérents au dépôt d'oxydes amorphes et de bénéficier des caractéristiques idéales d'un matériau cristallin, l'objectif est de réaliser l'épitaxie de la pérovskite LaAIO3, oxyde le plus prometteur au niveau structural et électronique. Ceci n'ayant jamais été accompli sur Si, il s'est avéré nécessaire d'effectuer un travail d'ingénierie d'interface en étroite collaboration avec une équipe spécialisée en épitaxie par jets moléculaires. En utilisant la Théorie de la Fonctionnelle de Densité, notre but est de déterminer la meilleure interface au niveau de la croissance et des propriétés électroniques. Nous avons ainsi construit et étudié plusieurs interfaces directes et couches d'accroche isolantes. D'une part, nos résultats montrent que certaines d'entre elles présentent d'excellentes perspectives de croissance pour l'oxyde. Notre interface la plus favorable, Al0. 5O1. 25, est élaborée en oxydant un motif de paires d'Al sur la surface Si(001). D'autre part, les discontinuités de bandes que nous avons calculées entre Si et LaAIO3 sont à la fois proches des valeurs expérimentales (avec LaAIO3 amorphe), bien que dépendant de la structure atomique de l'interface, et satisfaisantes pour une utilisation dans les futurs dispositifs MOS.
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Hatling, Oddmund. "Multiferroic, Magnetoelectric Nanoparticles : Lanthanum-substituted Bismuth Ferrite." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16315.
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In this report, 10 at% lanthanum was introduced to the perovskite structure of bismuth ferrite at the expense of bismuth through a modified Pechini wet chemical method. Green body powders were calcined at several temperatures, and the lattice parameters for each size were found by Rietveld refinement of X-ray powder diffraction data. The parameters displayed strong size-dependent properties, and the rhombohedral distortion from the cubic structure was reduced by decreased particle size. With decreasing crystallite size, the Néel temperature decreased and the cooperative cationic displacement (s - t) showed size dependence at crystallite sizes below 30 nm. A size-dependency was also observed in the Curie temperature.
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Hewage, Dilrukshi C. "SPECTROSCOPIC CHARACTERIZATION OF LANTHANUM-MEDIATED HYDROCARBON ACTIVATION." UKnowledge, 2015. http://uknowledge.uky.edu/chemistry_etds/54.
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Lanthanum (La)-promoted hydrocarbon activation reactions were carried out in a laser vaporization metal cluster beam source. Reaction products were identified by time-of-flight mass spectrometry, and the approximate ionization thresholds of La-hydrocarbon complexes were located with photoionization efficiency spectroscopy. The accurate ionization energies and vibrational frequencies of the La complexes were measured using mass analyzed threshold ionization (MATI) spectroscopy. Their molecular structures and electronic states were investigated by combing the MATI spectroscopic measurements with quantum chemical and Franck-Condon factor calculations.
In this dissertation, La-mediated C-H and C-C bond activation reactions were investigated for several small alkynes (acetylene, propyne) and alkenes (propene, 1,3-butadiene, 1-butene). The C-H bond activation was observed for both alkynes and alkenes and the C-C bond activation for alkenes. The metal-hydrocarbon intermediates formed by the C-H or C-C bond cleavage reacted further with one or more parent hydrocarbon molecules to produce larger species by C-C bond coupling reactions. Structural isomers of the intermediates and products were identified within an energy range of several kilocalories per mole. Reaction pathways for the intermediate and product formations were studied by theoretical calculations.
The ground electron configuration of La atom is 4d16s2.Upon the hydrocarbon coordination, La atom is excited to a 4d26s1 configuration to facilitate the formation of two La-C bonds. After the metal-hydrocarbon complex formation, only one electron is left in the 6s orbital of the metal center. Therefore, the most stable electronic state of the La complexes studied in this work is in a doublet spin state. Ionization of the doublet state yields a preferred singlet ion state. Although La is in the formal oxidation state of +2, the ionization energies of the metal-complexes are significantly lower than that of the free atom. This observation suggests that the concept of the formal oxidation state widely used in chemistry textbooks is not useful in predicting the change of the ionization energy of a metal atom upon ligation. Moreover, ionization has a very small effect on the geometry of the hydrocarbon fragment in each complex but significantly reduces the La-C distances as a result of an additional charge interaction.
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Cao, Wenjin. "SPECTROSCOPY AND FORMATION OF LANTHANUM-HYDROCARBON COMPLEXES." UKnowledge, 2018. https://uknowledge.uky.edu/chemistry_etds/106.
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Lanthanum-mediated bond activation reactions of small hydrocarbon molecules, including alkenes, alkynes, and alkadienes, were carried out in a laser vaporization metal cluster beam source. Time-of-flight mass spectrometry and mass-analyzed threshold ionization (MATI) spectroscopy, in combination with quantum chemical and multi-dimensional Franck-Condon factor calculations, were utilized to identify the reaction products and investigate their geometries, electronic structures, and formation mechanisms.
La-hydrocarbon association was only observed in the reaction of La with isoprene. C-H bond activation was observed in all reactions, hydrogen elimination was observed as the prominent reaction for the alkenes (2-butene, isobutene, 1-pentene, and 2-pentene), alkynes (1-butyne, 2-butyne, and 1-pentyne), and 1,4-pentadiene, and C-C bond activation was observed for the five-membered hydrocarbons (1-pentene, 2-pentene, 1-pentyne, isoprene, and 1,4-pentadiene).
The La-hydrocarbon radicals formed in these reactions had lanthanacyclic structures in various sizes, and each of the La-hydrocarbon complexes had a doublet ground state with a 6s1 La-based electron configuration. Ionization removed the 6s electron, and the resultant ion was in a singlet state. Formations of dehydrogenated products were either through a concerted hydrogen elimination process or the dehydrogenation after ligand isomerization. The C-C bond activation proceeded through La-assisted hydrogen migration, followed by C-C bond cleavage, or vice versa.
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Wong, Suk-yu. "Study of anti-cancer and anti-viral activities of lanthanide and vanadium complexes." View the Table of Contents & Abstract, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36584599.
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Guillot, Stéphanie. "Étude des paramètres principaux gouvernant les propriétés de conduction dans les apatites, électrolytes pour piles SOFC." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10052/document.
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Cette thèse a pour objet l’élaboration et la caractérisation d’oxyapatite silicatées de lanthane, matériaux potentiellement utilisables comme électrolyte pour piles à combustible à oxyde solide. Des poudres et céramiques denses d’apatite de stœchiométries en oxygène et de compositions (substitutions) différentes ont été élaborées par réaction à l’état solide à haute température. Il ressort que quelque soit la composition, le paramètre principal qui gouverne les propriétés de conduction est la stœchiométrie en oxygène. La conductivité atteint 1,7 x 10-2 S.cm-1 à 700°C pour la composition La10Si5,5Mg0,5O26,5. La combinaison d’analyses spectroscopiques (Diffusion Raman, Résonance Magnétique Nucléaire) et de diffraction des neutrons a permis de définir un mécanisme de conduction des ions oxydes dans la structure. L’existence d’un site interstitiel localisé dans les canaux de la structure apatite en (-0,01, 0,04, 0,06) est confirmée. Un chemin de diffusion des ions oxyde de type « lacune sur le site 2a – atome interstitiel » est proposé le long de l’axe c. Ce mécanisme semble facilité par le déplacement des tétraèdres situés à la périphérie du canalThis work is devoted to the elaboration and the characterisation of apatite type lanthanum silicates as new electrolyte for SOFC fuel cells. Apatite powders and dense ceramics with different oxygen stoichiometries and compositions (substitutions) were prepared by high temperature solid state reaction. Whatever the composition, we can conclude that the key parameter which governs the conduction properties is the oxygen stoichiometry. The conductivity reaches 1.7 x 10-2 S.cm-1 at 700°C for the La10Si5,5Mg0,5O26,5 composition. By combining Raman spectroscopy, NMR and neutron diffraction, an oxide ion conduction mechanism was deduced. The existence of an interstitial site located at (-0.01, 0.04, 0.06) was confirmed. This allows to proposed a realistic oxygen diffusion pathway through this interstitial site along the c axis. Moreover, this mechanism seems to be facilitated by the displacement of tetrahedral located at the periphery of the oxide channels
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Berche, Alexandre. "Contribution à l'étude thermodynamique du système Lanthane - Magnésium - Zinc (La-Mg-Zn)." Aix-Marseille 3, 2007. http://www.theses.fr/2007AIX30084.
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Les alliages La-Mg-Zn, de par leurs faibles masses volumiques, sont des matériaux de structure intéressants pour l'industrie des transports. L'évolution de la stabilité des phases en température doit donc être connue. Le but de ce travail a été de mener à bien l'étude complète du diagramme de phases La-Mg-Zn dont la connaissance bibliographique n'était que fragmentaire. Pour cela, de nombreux alliages ont été élaborés et caractérisés sous atmosphère contrôlée. Les phases en présence ont été mises en évidence par Diffraction RX et microsonde. Des mesure enthalpiques ont été effectuées par calorimétrie de dissolution et comparées à des résultats obtenus par DFT. Les évolutions des équilibres avec la température ont été observées par ATD 1500K. La cohérence de l'ensemble de ces nouvelles données diagrammatiques et énergétiques rend possible l'optimisation thermodynamique du système, facilitant ainsi la mise au point de futurs alliages industrielsThe La-Mg-Zn alloys, due to their density, could be used as structural materials for the transport industry. The evolution of the stability of phases with respect to temperature has thus to be perfectly known. Since the phase diagram of this system has been elsewhere scarcely studied so far, the purpose of this work was to reinvestigate it. Thus, many alloys were prepared and characterized under controlled atmosphere. X ray diffraction and microprobe analysis were performed to identify the phases. The formation enthalpies were determinedby calorimetry and compared to thoses calculated by DFT. The evolution of the equilibrium with the temperatures were identified by DTA - 1500K. This large number of new and coherent data on the La-Mg-Zn system makes possible the thermodynamic assessment of the phase diagram and may help the developpment of future industrial alloys
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Huang, An-Rong. "Synthèse par procédé sol-gel du chromite de lanthane pour éléments chauffants." Montpellier 2, 1995. http://www.theses.fr/1995MON20039.
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Des poudres de chromite de lanthane ont ete preparees par procede sol-gel en milieu aqueux a partir de deux precurseurs: nitrates ou acetates. Les sols colloidaux ont ete obtenus par precipitation et peptisation en ajoutant de l'ammoniaque. Les zones de ph de precipitation et de peptisation ont ete determinees par des dosages acidobasiques. Apres gelification a l'air, la decomposition des gels a ete etudiee par analyse thermique (atg - atd) et par spectroscopie ir ; la cristallisation du chromite de lanthane, obtenu par traitement thermique des gels a ete determinee par diffractometrie des rx sur poudre. Des elements chauffants tubulaires ont ete realises par la methode d'extrusion avec les poudres ainsi obtenues. La composition de pates ceramiques permettant cette mise en forme a ete determinee. Une analyse thermomecanique par dilatometrie a permis de suivre le comportement au frittage des preformes, et de determiner la temperature de frittage convenable pour differentes compositions. Les poudres et les ceramiques ont ete caracterisees par meb, bet, porosimetrie a mercure, et par la mesure de la conductivite electrique
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Maurin, Isabelle. "Effets de non-stoechiometrie et de granularite dans les manganites de lanthane." Palaiseau, Ecole polytechnique, 2000. http://www.theses.fr/2000EPXX0004.
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La magnetoresistance geante (mrg) des manganites de structure perovskite pourrait ouvrir leur champ d'application a la detection magnetique. Les champs necessaires a des variations de resistance consequentes restent cependant trop eleves. L'objet de ce travail est l'etude des proprietes magnetoresistives des manganites granulaires qui revelent une composante mr bas champ au-dessous de leur temperature de curie, effet commun aux materiaux ferromagnetiques polycristallins. Des ceramiques ont ete elaborees par chimie douce, pour des tailles de grains comprises entre 20 nm et 10 m. Ces grains sont assimilables a des heterostructures cur-coquille. Pour les plus faibles tailles de grains, la contribution de la surface domine. Une seconde transition isolant-metal apparait et les courbes de resistivite sous champ presentent une hysteresis differente de celle des cycles d'aimantation. La connexion entre grains a ete modifiee par irradiation aux electrons. Il y a alors endommagement des joints de grains, les paires de frenkel s'y formant preferentiellement ou venant s'y segreguer au recuit. Une partie des jonctions sont rompues, induisant des effets de percolation et une augmentation de la composante mr bas champ au voisinage de la transition ferromagnetique. Les echantillons synthetises a basse temperature presentent des lacunes cationiques. Pour separer les effets de granularite et de non-stchiometrie, le systeme non substitue la 1 xmn 1 xo 3 a ete etudie. Pour des teneurs croissantes en lacunes, les spectres d'absorption des rayons x au seuil k du manganese montrent un deplacement du seuil d'absorption vers les hautes energies, indiquant une augmentation de la densite de porteurs de charge. Ces defauts ne conduisent toutefois pas a un dopage type aliovalent. L'analyse quantitative des spectres demontre le piegeage d'une partie des porteurs pour les fortes teneurs en defauts. Il y a egalement reduction de la mobilite des porteurs libres, d'apres des mesures d'effet seebeck.
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Negahdari, Zahra [Verfasser]. "Reaction Sintered Alumina/Lanthanum Hexaaluminate Composites / Zahra Negahdari." Aachen : Shaker, 2010. http://d-nb.info/1124365702/34.
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Park, Hyun. "Fabrication of lanthanum copper oxide nanofibers by electrospinning." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0009920.
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Skellern, Matthew G. "Structural and electronic properties of barium lanthanum vanadates." Thesis, University of Aberdeen, 2003. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU167989.
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A study of the subsolidus region of the BaO-La2O3-V 2O5 phase diagram has been carried out. Four ternary phases can be prepared, one of which has not been previously identified. The four ternary phases are a palmierite solid solution Ba3-3xLa2x V2O8, Ba2LaV3O11, BaLa10V4O26 (new phase) and Ba3La 40V12O93. Addition of BaLa10V 4O26 and the previously omitted phase La1.42V 0.58)3.58 to the ternary system has resulted n a re-determination of the complete phase diagram. A comprehensive study of the Ba3-3xLa 2xV2O8 solid solution has been carried out, employing a number of techniques including x-ray diffraction, infra-red spectroscopy, thermogravemetric analysis, impedance spectroscopy, electron paramagenetic resonance spectroscopy, inductively coupled plasma mass spectroscopy and x-ray absorption near edge structure spectroscopy. Conductivity measurements show the end-member Ba3V2O8 to be an oxide ion conductor, with the conduction mechanism being facilitated by the ease of transformation of the BaO3 layers to BaO2 and vice versa. The La-doped members show an increase in conductivity, with electrons becoming the dominant conducting species. The crystal structure of Ba2LaV 3O11 was confirmed to be isostructural with Ba2BiV 3O11. A full refinement of the structural parameters has been performed. The unit cell is primitive monoclinic, a = 12.44510(3)A, b = 7.78854(12)A, c = 11.26245(21)A and beta = 103.134(4)°, space group P21/c. Preliminary structural studies have begun on the new phase BaLa10V4O26. The x-ray powder pattern has been fully indexed and a possible monoclinic unit cell of a = 20.2939A, b = 5.886A, c = 12.6234A and beta = 118.05° is proposed. The serendipitous synthesis of a barium-deficient celsian phase, Ba0.8A11.6 Si2.4O8, is reported; the structure was solved using Patterson methods. The phase has a monoclinic unit cell with, a = 8.6090(8)A, b = 13.0858(12)A, c = 7.2047(7)A and beta = 115.418(2)°, space group C2/m.
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Henneberg, Eva. "Thermodynamische und kinetische Untersuchungen im System La-Si-H-(Cl)." Doctoral thesis, [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969828241.
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Dürr, Ines Anne [Verfasser], and Caroline [Akademischer Betreuer] Röhr. "Binäre und ternäre Lanthan-Triel-Tetrel-ide : : Synthese, Kristallchemie und chemische Bindung." Freiburg : Universität, 2012. http://d-nb.info/1123470995/34.
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Bentz, Dirk. "Komplexe von Zink, Cadmium, Lanthan, Cer und Samarium mit sperrigen Alkylcyclopentadienyl-Liganden." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=977288579.
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Gömann, Anissa. "Das Verhalten von donatordotierten SrTiO3-Oberflächen unter Hochtemperaturbehandlung." Clausthal-Zellerfeld : Papierflieger, 2005. http://deposit.d-nb.de/cgi-bin/dokserv?idn=974496510.
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Souza, Raquel Aparecida De. "Étude de l'effet des corrélations électroniques et magnétiques dans le nickelate de lanthane." Thesis, Tours, 2008. http://www.theses.fr/2008TOUR4033/document.
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Les propriétés de La2 NiO4+d et de La2 CuO4+d supraconducteur dépendent du dopage en trous. Des ordres de charges et spins sont reportés dans ces systèmes. La relation entre la formation de cet ordre et l'absence de la supraconductivité dans les nickelates ne sont pas éclaircis. Dû à la stabilité de l'ordre dans les nickelates, ce système a été choisi pour caractériser les fluctuations de spins. RPE et susceptibilité magnétique ont permis de mettre en évidence des modifications de fluctuations magnétiques dans La2-xSrxNiO4+d . L'ordre des oxygènes, 3D ou 1D, la structure cristalline et l'origine des trous influent sur le type de mise en ordre caractérisé. Deux signaux RPE, attribués à des polarons magnétiques liés à l?ordre des charges et à des clusters de spins Ni, ont été observés. Conductivité optique et diffraction neutronique sur un monocristal ont complété l'étude. Des résultats nouveaux, qui ne contredisent pas une mise en ordre de charges dans ce système, ont été mis en avantThe properties of La2-x Srx NiO4+d , isostructural with the superconducting cuprates, strongly depend on the doping. As for the superconducting system, stripe charge and spin order were reported. Stripe formation, the relation between nickelates and cuprates, and the absence of superconducitivity in nickelates is not a clear question. Due to the stability of the order in nickelates, the study of spin ?uctuations in this system has been chosen in order to get information about the system dynamics. ESR and magnetic susceptibility showed evidences of magnetic ?uctuations on La2-x Srx NiO4+d system with different doping. Oxygen order, 3D or 1D, crystal structure and origin of doped holes have an in?uence of the type of order observed. Resonance signals attributed to magnetic polarons and Nispin clusters have been detected. Optical conductivity and neutron diffraction completed the study a single crystal, which present new features, but do not contradict the charge order in the system
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Sbata, Mouna. "Application de la chimie quantique à la spectroscopie structurale et à la dynamique radiative de LaF+ et GaH." Lille 1, 1999. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1999/50376-1999-135.pdf.
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Les calculs ab initio de chimie quantique sont un apport appréciable pour la spectroscopie structurale des molécules et la dynamique radiative se produisant au sein de ces systèmes. Des calculs de type SCF-MRCI ont servi à déterminer la structure électronique des états doublets spectroscopiquement accessibles de LaF + et de confirmer les symétries de l'état fondamental (X²[Delta]) et du premier état excité ( ²[Sigma]+ ), contrairement à l'ordre énergétique observé dans la molécule neutre isovalente LaO. D'autres calculs d'interaction de configurations prenant en compte dès l'ordre zéro le couplage spin-orbite ont permis de déterminer avec précision la structure fine de GaH. Nous avons calculé les moments de transition vibroniques, les coefficients d'Einstein, les forces d'oscillateurs relatifs à des transitions observées ou non observées de GaH et LaF+ puis les durées de vie radiatives des premiers niveaux vibrationnels des états électroniques calculés. Utilisant un modèle simple d'oscillateurs harmoniques couplés, nous avons montré que le r-centroïde d'une interaction lié (v=0)-continuum était situé à la distance d'équilibre de l'état lié. Enfin, nous avons interprété le dédoublement-[Lambda] inhabituel observé dans l'état a3[Pi] de GaH grâce à une méthode de déperturbation originale qui relie directement l'effet à des différences de constantes rotationnelles.
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Depentori, Francesco [Verfasser]. "Charakterisierung der lokalen Korrosionseigenschaften von lanthan- und neodymmodifizierten (alpha-beta) Titanlegierungen / Francesco Depentori." Aachen : Shaker, 2014. http://d-nb.info/1049379551/34.
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Devenson, Jelena. "Fabrication and investigation of heterostructures based on lanthanum manganites." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091008_155508-20318.
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In this dissertation application of the lanthanum manganite films and their heterostructures for fabrication of new spintronic devices is discussed. The main subjects of this work are the junctions between lanthanum manganite oxide thin films doped by divalent (Ca, Ba, Sr) and tetravalent (Ce) ions as well heterojunctions formed between lanthanum manganites and n-type SrTiO3Disertacijoje nagrinėjamos įvairios galimybės panaudoti feromagnetinių oksidų – manganitų sluoksnius bei jų darinius naujų spintronikos prietaisų gaminimui. Šio darbo pagrindiniu tyrimo objektu pasirinktos sandūros, sudarytos tarp dvivalenčiais (Ca, Ba, Sr) ir keturvalenčiais (Ce) jonais legiruotų lantano mangano oksidų plonųjų sluoksnių, o taip pat tarp manganitų ir elektroninio laidumo SrTiO3
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Hurst, Phillip C. "Lanthanum (III)-promoted clevage of RNA and cyclic nucleotides." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=34740.
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The RNA dimer ApA is rapidly cleaved in the presence of lanthanum(III) chloride yielding the products of transesterification and hydrolysis, 2 '-AMP, 3'-AMEP and adenosine. The intermediate 2,3'-cAMP does not accumulate. Under pseudo-first-order conditions (approximately 100-fold excess lanthanum(III) chloride) the half-life for ApA cleavage is only 13 seconds.The potentiometric titration, pH-rate profile and dependence upon lanthanum(IIII) chloride concentration support a penta-mu-hydroxo dilanthanum species as the active species. The kinetic isotope effect of 1.9 and a one-proton inventory indicate that the 2'-hydroxyl deprotonation is not concerted with the nucleophilic attack. It is proposed that a rapid equilibrium proton transfer occurs between the 2'-hydroxyl and a bridging hydroxo prior to the nucleophilic attack and rate-determining intramolecular general acid catalyzed breakdown of the phosphorane to products. It is proposed that the general acid is a bound water, formed from the protonation of the bridging hydroxo.
Lanthanum(III) ion was found to be among the best of the trivalent lanthanides for promoting ApA cleavage, contrary to literature reports. The proposed lanthanide dimer mechanism, which is consistent with the behavior of the other lanthanides, easily explains this.
The lanthanum(III) dimer was also found to be highly reactive towards the DNA model compound bis(p-nitrophenyl) phosphate and the cyclic nucleotides 3',5'-cAMP and 2',3'-cAMP, providing half-lives of 12s, 9min and 340ms respectively. The results were consistent with a bound mu-hydroxo as the nucleophile.
The results for the ApA and cyclic nucleotides reactions are faster than any reported for synthetic catalysts.
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Hurst, Phillip C. "Lanthanum(III)-promoted cleavage of RNA and cyclic nucleotides." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0015/NQ44460.pdf.
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Petrovich, Marco. "Gallium lanthanum sulphide glasses for near-infrared photonic applications." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/15477/.
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This thesis investigates gallium lanthanum oxysulphide (GLS) glasses for potential fibre device applications. GLS glasses have low phonon energy and high rare earth solubility, which makes them candidates for rare earth-doped devices, and in particular for the 1.3 µm praseodymium-doped optical fibre amplifier. In addition, they have one of the highest nonlinear figures of merit among optical glasses, and therefore have potential for all-optical switching and other nonlinear devices. Practical applications, however, have been prevented by the impossibility, to date, of achieving single mode fibres with low attenuation. Previous efforts were concentrated on fabrication and especially tried to address the known issues of glass purity and thermal stability. The present work is focussed on assessing the fundamental glass transparency and on the mechanisms affecting the transmission loss of GLS glasses. The optical absorption at 1.55 and 1.7 µm was measured for the first time by laser absorption calorimetry using a tunable free electron laser source. To this end, a calorimeter was designed and commissioned and an improved model for the heat flow analysis of laser calorimetry was also developed. Our measurements identified optical absorption as the principal near-IR loss mechanism for GLS glasses. The extrinsic absorption due to transition metal ion impurities was also measured, and the presence of the weak absorption tail, due to absorption from gap states, was investigated. The occurrence of photoinduced effects and their impact on the material?s transmission wak also analysed. A thorough characterisation of the photodarkening and photoinduced absorption due to bandgap illumination, including its dependence on the excitation wavelength, and the kinetics of its formation, decay and reversibility, was achieved. Finally, the response of GLS glasses to high-intensity irradiation in the 1 µm wavelength region was studied and photoinduced darkening was observed to occur in low oxide undoped and Pr3+-doped GLS. All these topics are of great practical relevance. The present work clearly demonstrates that, in addition to the known fabrication challenges of monomode GLS fibres, careful consideration of the intrinsic transparency and photoinduced effects is essential for their successful application in fibre devices.
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Palan, Rohit Chandulal. "Pyroelectric Properties of Ferroelectric Lanthanum Bismuth Titanate Thin Films." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1000746504.
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Morrison, Finlay D. "Synthesis and electrical characterisation of lanthanum doped barium titanate." Thesis, University of Aberdeen, 1999. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU551388.
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Lanthanum is one of the most common so-called "donor-dopants" for BaTiO 3. Combined synthesis, phase diagram and electrical studies of La-doped BaTiO3 ceramics were undertaken to determine the doping mechanisms(s) and to understand the unusual resistance behaviour of air-heated ceramics. Charge compensation was found to be maintained via the creation of Ti vacancies, resulting in the solid solution Ba1-xLax Ti1-x/4O3 with x ≤ 0.25 at 1350[Special character omitted]C. No evidence for the existence of the commonly cited La-"donor-doping" or barium vacancy mechanisms was observed. ac Impedance spectroscopy on samples heated in O 2 at 1350[Special character omitted]C indicated the presence of insulating bulk and grain boundary components. The tetragonal cubic and orthorhombic tetragonal phase transition temperatures, Tc and To/t, respectively, decreased dramatically with increasing x, the former approximately linearly at a rate of dTc/dx ca. 0.24 [Special character omitted]C/x. The value of 'max at T c increased with x for 0 ≤ x ≤ 0.06 and reached a value > 25,000 at ca. -9 [Special character omitted]C. For x ≥ 0.08, Tc and To/t coalesce and, with increasing x, ' max decreased and "relaxor"-type, frequency-dependent ' behaviour was observed. The semiconductivity observed in air-heated samples was attributed to oxygen loss. Combined impedance and modulus spectroscopy of samples heated in air showed all samples to be electrically inhomogenous, however, all contained a semiconducting bulk component with an associated resistance < ca. 20O. The total dc sample resistance was dependent on the level of re-oxidation during cooling and was dominated by insulating thin layer regions. Two oxidised thin layer effects were identified. At low La concentrations, e.g. x = 0.03, re-oxidation occurred at the grain boundaries and on individual grain surfaces whereas the grain interiors remained semiconducting. At higher La concentrations, e.g. x = 0.20, re-oxidation occurred preferentially at pellet surfaces whereas the pellet interior remained semiconducting. The observed room temperature resistance anomaly for air-heated La-doped ceramics is not linked to La-"donor-doping" but is an artefact of sample processing which results from oxygen loss during heating to high temperatures, > 1200 [Special character omitted]C.
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Turcaud, Jeremy. "Magnetocaloric effect and thermal transport management in lanthanum manganites." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/40889.
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This thesis investigates two challenges associated with the use of manganites for magnetocaloric applications. The first challenge is associated with methods to engineer the thermal conductivity, K. The second challenge is to understand the limits of the entropy change achievable in magnetocaloric manganites. Thermal management has been achieved via different microstructuring routes and their influence on thermal transport properties such as K, resistivity and thermopower, have been studied. A factor of two increase in K is demonstrated by using density and grain size optimization, while three-fold and six-fold increases are seen by employing the introduction of a second highly conductive phase via: (1) silver impregnation and silver particle coating and (2) copper electroplating, respectively. Understanding the magnetocaloric effect (MCE) characteristics in manganites has been achieved by bringing together magnetisation, magneto-structural, magneto-Seebeck, and neutron diffraction independent measurements. We first show that the temperature T* up to which a spontaneous magnetisation is observed in the inverse magnetic susceptibility of La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 above Tc, is related to the transition temperature of the low temperature (high-magnetic field and high-magnetisation) magnetic phase. In the most widely studied La(1-x)CaxMnO3 (x = 0.2, 0.25, 0.3), we then conclude that unlike between the degree of static Jahn-Teller distortion and the interval [T*-Tc]/Tc where we show that there exists a close relationship, there is no apparent correlation between the magnitude of the MCE and [T*-Tc]/Tc . We then unravel the competing strength of the various degrees of freedom and show that the inhibition of a large magnetocaloric response is due to the strong correlations that underpin the collosal magnetoresistance effect: both clustering of magnetic Mn atoms due to polaron formation and the insulator to metal transition. Finally we discuss prospects to improve material properties for application in light of these findings.
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Jorgensen, Mette Juhl. "Lanthanum manganate based cathodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343243.
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