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<p>Phase change materials (PCMs) has emerged as advanced functional materials for efficient thermal energy storage and release. Compared to other organic and inorganic PCMs, oxide-based PCMs have attracted growing interest because of small volume expansion, minor leakage issue, and moderate latent heat. In this dissertation, two special cases of oxide-based PCMs is discussed, i.e., vanadium dioxide (VO₂), and Bi-based perovskite/supercell structures. Specifically, VO₂ emerges as a focus of research because of its well-known semiconductor-to-metal transition (SMT) upon heating close to 68 °C. The intrinsic coupling of SMT and R-M1 structural change makes VO₂ a favorite material both scientifically interesting and technologically important for potential sensor and memory device applications. On the other hand, BFMO supercell structure originates from the double-perovskites, while the substrate-induced epitaxial strain induces the stacking and commensurate modulations of Fe/Mn double layers. The significantly enhanced multiferroic response is attributed to its non-centrosymmetric structure.</p> <p>In this dissertation, a comprehensive study on the FM integration and novel approaches to achieve broad range transition temperature (<em>T</em>_<em>c</em>) tuning is explored in VO₂ thin films. Specifically, three novel metal/VO₂ nanocomposite designs are discussed, i.e., Pt/VO₂, Ni/VO₂ and Li/VO₂, with different morphology and Tc tuning mechanisms. First, by reconstructing the energy band structure at the metal/VO₂ interface, bidirectional <em>T</em>_<em>c</em> tuning in Pt/VO₂ nanocomposites can be achieved owing to the size dependent work function of Pt NPs. Next, by engineering the morphology by lattice matching, diffusion kinetics, and interfacial mixing, the exploration on Ni/VO₂ nanocomposites achieve the combined goals of Tc tuning and magnetic incorporation/magneto-optical (MO) coupling. Finally, by varying Li concentration during the metal-ion intercalation, <em>T</em>_<em>c</em> of both VO₂(B) and VO₂(M1) thin films can be systematically tailored because of structural deformation and the change in charge carrier density. The demonstration of metal/VO₂ nanocomposite thin films reveals a promising approach to fulfill various working environments for VO₂-based novel electronics, photonics, and spintronics. Furthermore, the microstructure evolution of the ultrathin BFMO supercell structure as well as its physical properties is first studied. The robust ferromagnetic and ferroelectric response is preserved in the ultrathin structure less than 10 nm, making it an attractive candidate for next-generation spintronics based on 2D materials.</p>

<p> A brief review of the industrial methods employed to remove hydrogen sulfide from contaminated gas streams is given, with particular emphasis centred on the Stretford process.</p> <p> A summary of some recent developments in the solvent extraction of vanadium(5) is also given, together with the relevant aqueous vanadium chemistry.</p> <p> The experimental section deals with the development and optimization of an analytical procedure for vanadium(5) determination in alkaline solution. This developed procedure is then applied to the analysis of Stretford liquor.</p> / Thesis / Master of Science (MSc)

The Norrbotten region is an important Swedish mining district with occurrence of several economic deposits and sub-economic deposits of apatite iron ores (Kiruna Type) and epigenetic Cu-Au ores. The apatite iron ores include the large Malmberget deposit mined by LKAB company as one of their world class underground mines. The Malmberget ores are hosted by a Paleoproterozoic unit of metavolcanics and metasedimentary rocks intruded by multiple plutonic rocks varying in composition. The rocks at Malmberget are overprinted by intense widespread hydrothermal alteration, metamorphism and deformation. The Malmberget iron deposit is thought to originally be one continuous lens that segmented into more than 20 different orebodies during the regional metamorphism and deformation. The Malmberget deposit is characterized by different orebodies that shows different textures and chemical variations. The iron ores at Malmberget are mainly consisting of magnetite and hematite.   Apatite iron ores of the Kiruna type have raised divergent opinions regarding whether this type of deposits are magmatic or hydrothermal in origin. However, trace element analysis have been used for studies that yield information about ore-forming fluids and mineralizing processes. This paper aims at understanding the vanadium behaviour and distribution in the Malmberget ores as well as studying textural and mineralogical control of vanadium in the iron ores. Learnings from this paper aids in understanding the controls and distribution of vanadium and increasing knowledge regarding genetic aspects of the Malmberget deposit. To achieve this, detailed core logging, optical microscopy, lithogeochemistry and scanning electron microprobe analyses were utilized to figure out why the vanadium content is high in some places and low in other parts of the deposit.  Textural data of both magnetite and hematite ores show that the Malmberget ores can be characterized as massive ore and breccia type. The ores in the western part of the deposit are dominated by metamorphic and oxidation textures, including martitisation textures and triple junction textures. The ores in the eastern part are mainly massive magnetite textures with apatite and amphibole as the main gauge minerals. Metamorphic recrystallization and oxidation of the ores resulted in vanadium redistribution and chemical changes of both hematite and magnetite. Vanadium is high in both magnetite and hematite ore and low in the silicate host rocks. The eastern ore bodies of the deposit are found to be higher in vanadium content compared to those on the western side. Vanadium is high in magnetite ore sections but in magnetite-hematite grain pairs vanadium is redistributed from the magnetite grain to the adjacent hematite grain during metamorphic oxidation and recrystallization of magnetite. The results from this project suggest that a better understanding of what controls the distribution of vanadium in the ores needs more investigations regarding element partition under different geochemical conditions. There are also uncertainties regarding the initial source of vanadium and its primary distribution in different minerals and ore types and later redistributions. The origin of hematite in the ores and the stratigraphic position of the ores are other aspects that needs further studies to get a deeper understanding of the behaviour of vanadium in the Malmberget deposit.

No description available.

No description available.

Dans le milieu marin, les émissions biogéniques de composés iodées jouent un rôle essentiel dans le cycle biogéochimique de l’iode. Cependant les processus enzymatiques responsables de l'absorption, du stockage ou de la synthèse de métabolites iodés restent mal connus chez les chez les organismes marins, et plus encore chez les bactéries. Plusieurs gènes, potentiellement impliqués dans le métabolisme de l’iode, ont été identifiés dans le génome de la bactérie marine, Zobellia galactanivorans, dont celui codant une iodoperoxydase à vanadium (VIPO), enzyme spécifique de l'oxydation des iodures. La partie principale du projet de thèse a consisté à comprendre les mécanismes moléculaires contrôlant la spécificité pour certains halogénures des haloperoxydases à vanadium, en étudiant la VIPO de Z. galactanivorans par des approches de mutagénèse dirigée et de biologie structurale. Les douze enzymes mutantes produites et caractérisées au niveau biochimique montrent soit une perte d’activité, soit des modifications de leurs propriétés catalytiques, soit encore une faible activité bromoperoxydase. Les enzymes sauvage et mutantes ont également été étudiées par diffraction et absorption des rayons X, afin de relier les modifications structurales à leurs propriétés catalytiques. Les résultats suggèrent que le principal facteur modulant la spécificité chez ces enzymes est le potentiel d’oxydoréduction de l’intermédiaire réactionnel, le peroxovanadate. Des analyses biochimiques ont aussi été entreprises pour deux autres protéines identifiées sur le génome de Z. galactanivorans. La première protéine s’est révélée être une seconde VIPO. Pour la deuxième protéine, similaire à une iodotyrosine déiodinase, l’activité biochimique reste encore à être caractérisée. Z. galactanivorans posséderait plusieurs enzymes pouvant oxyder l’iodure, ainsi qu’une permettant de cliver les liaisons C-I. En parallèle à ce travail, la localisation et la spéciation de l’iode ont été étudiées par imagerie chimique chez Z. galactanivorans et chez l’algue brune, Laminaria digitata, connue pour ses fortes teneurs en iode. Les résultats de ce travail apportent un nouvel éclairage sur les mécanismes contrôlant la spécificité des haloperoxydases à vanadium envers les halogénures, et également sur l’origine bactérienne de cette famille d’enzymes. Plus globalement, ces études permettent de mieux appréhender le rôle du métabolisme de l’iode chez certaines bactéries marines et leurs importances dans le cycle biogéochimique de l’iode. / In marine environment, biogenic emissions of iodinated compounds play an essential role in biogeochemical cycle of iodine. Nevertheless, enzymatic process involved in absorption and storage of iodine or in the synthesis of iodinated compounds are unknown marine organisms, especially in bacteria. Several genes, potentially involved in iodine metabolism, have been identified in the genome of a marine bacterium, Zobellia galactanivorans. One of these genes codes for a vanadium iodoperoxydase (VIPO), an enzyme specific of iodide oxidation. The main part of the thesis project was to understand molecular mechanisms controlling the specificity vanadium halopéroxydase (VHPO) for some halide, by studying the VIPO from Z. galactanivorans by directed mutagenesis and structural biology. To lead this project, twelve mutated enzymes were produced and characterized at biochemical level. For some of them, mutations lead to a loss of activity or to modification of catalytic properties or to a slight VBPO activity. The wild type enzyme and three mutants were also analyzed by X ray absorption and diffraction spectroscopy in order to link the structural modifications to their catalytic properties. The results of this study suggest that the main factor modulating the specificity in these enzymes is modification of redox potential of the peroxovanadate. Biochemical analyses lead with two other proteins identified in the genome of Z. galactanivorans. The first protein was characterized as a new VIPO. For the second protein, similar to mammal iodotyrosine deiodinase, the biochemical activity remains to be characterized. Z. galactanivorans seems to have several enzymes which oxidize iodide or split C-I bond. In parallel at this work, the localization and speciation of iodine were analyzed by chemical imaging in Z. galactanivorans and in the kelp L. digitata, known to concentrate highly iodide. All this information allow to a better understanding of molecular mechanisms involved in the specificity for halide in VHPO and the bacterial origin of these proteins. More generally, these studies assess to understand the role of iodine metabolism in some marine bacteria and there role in biogeochemical cycle of this element.

Des couches minces d'oxyde de vanadium, V2O5, ont été déposées à température ambiante sur substrat ITO/verre en utilisant trois conditions de dépôt différentes, à savoir la pulvérisation cathodique par magnétron haute fréquence (RFMS) avec cible métallique en V (métal V2O5RF) et cible d’oxyde de V2O5 (oxyde V2O5RF) et la pulvérisation cathodique par magnétron en régime d’impulsions de haute puissance (HiPIMS) avec cible métallique (V2O5HiPIMS), respectivement. L’optimisation des différents paramètres de dépôt conduit à une modulation de la structure et morphologie des films, d’amorphes à cristallisés et de denses à poreux. Le cyclage en milieu lithié ou sodé montre un multichromisme associé à un changement réversible de coloration impliquant 4 couleurs, orange, vert, bleu et gris, en fonction des états de réduction et d’oxydation. Un cyclage prolongé sur 1000 CV, indique une différence de stabilité en fonction de la méthode de dépôt. Les films denses déposés par HiPIMS présentent une grande stabilité tandis qu’une dégradation très rapide est observée pour les films amorphes (oxyde V2O5RF) et qu’une augmentation de capacité est observée pour les films (métal V2O5RF). Ces différences de comportement sont attribuables à des différences de morphologie faisant apparaitre des films fissurés et fragiles dans un cas et denses sans grande évolution dans l’autre cas. Par ailleurs, le cyclage longue durée entraine une amorphisation des films. La caractérisation par un grand nombre de techniques (GIXRD, XPS, TOF-SIMS, AES et RBS / NRA) des différents comportements au cours du processus électrochrome a mis en évidence que le mécanisme ne peut être simplement décrit par une unique réaction d’insertion/désinsertion. Les propriétés électrochromes prometteuses des couches unitaires de V2O5 (métal V2O5RF) ont permis leur intégration dans des dispositifs complets à base d’électrolyte transparent ou opaque. Ainsi, des dispositifs WO3/V2O5 et V2O5/V2O5 ont été caractérisés pour des applications vitrage et afficheur. / Vanadium oxide thin films were deposited on ITO coated glass substrate at room temperature using three different deposition conditions, namely radio frequency magnetron sputtering (RFMS) with V metallic target (V2O5RF-metal) or V2O5 oxide target (V2O5RF-oxide) and High Power Impulse Magnetron Sputtering (HiPIMS) with V metallic target (V2O5HiPIMS), respectively. Significant difference in structure and morphologies are reported. V2O5RF-metal films are crystalline and dense with a disturbed surface which is thickness dependent, while V2O5RF-oxide and V2O5HiPIMS films are amorphous and porous or dense respectively. V2O5 thin films show reversible electrochromism with 4 colors, which are orange, green, blue and gray, in reduction/oxidation states when cycled in Li and Na based electrolytes. However, depending on the deposition method, V2O5 films show different cycling stability, recorded up to 1000 cycles, that is attributed to a modification of the morphology (i.e. increase of the surface area due to cracks and increase porosity, as well as a progressive amorphization particularly in lithium electrolyte. The different behaviors during the electrochromic process were investigated with GIXRD, XPS, TOF-SIMS, AES and RBS/NRA indicating a mechanism more complex than a simple insertion/deinsertion. Finally, two types of ECDs using either transparent electrolyte membrane or opaque are fabricated coupling V2O5 thin films to WO3 or to V2O5 in a symmetrical device aiming at application in smart windows and displays, respectively.

Les travaux réalisés lors de cette thèse ont pour objectif la fabrication de filtres accordables fort Q0. Pour cela nous nous sommes naturellement orienté vers des structures volumiques puisque elles permettent l’obtention de Q0 important. Nous avons également utilisé des éléments d’accord permettant de maximiser ce Q0, tels que des MEMS-RF ou bien encore des patchs de Matériaux à Transition de Phase (PTM) comme le dioxyde de vanadium (VO2). Nous avons démontré lors de notre étude que ces dispositifs garantissaient des Q0 supérieurs à 1000 sur une large plage d’accord. / This work is based on the fabrication of High-Q tunable filters. We looked at cavity filters since they allow us to achieve a high Q0. We also used RF-MEMS or vandium Dioxyde as tuning element. Since they provide a high-Q tuning. We have demonstrated Q0 better than one thousand over a wide tuning range.

Dans l'objectif de combler le gap entre l'offre et la demande en propène, la réaction d'oxydation déshydrogénante du propane (ODHP) est une solution alternative à la réaction de déshydrogénation directe. Les hydroxyapatites (HAp) modifiées au vanadium sont des matériaux bi-fonctionnels aux propriétés acido-basiques et redox intéressants pour cette réaction. L'objectif de cette thèse est d'étudier le comportement catalytique de ces systèmes et d'établir des relations entre structure et réactivité. Par le contrôle des conditions de synthèse et pourvu que le pH soit maintenu élevé (~9), la solution solide Ca10(PO4)6-x(VO4)x(OH)2 est obtenue dans toute la gamme de composition (x 0→ 6), alors que pour un pH inférieur, un mélange de phases d'HAps au vanadium et de Ca2V2O7 est obtenu pour x ≥ 4. Pour la solution solide, contrairement à la sélectivité en propène, la conversion en propane n'augmente pas avec la teneur en vanadium non exposé en surface. L'activation de la liaison C-H du propane s'explique par une propriété intrinsèque à la structure HAp, en lien avec la formation thermiquement activée d'anions O2- très basiques. Leur formation in situ résulte de la déshydratation progressive des colonnes d'ions OH- via le processus de conduction ionique par les protons, exalté sous conditions réactionnelles. L'organisation du vanadium sous la forme de tétramères dans Ca2V2O7 au lieu de tétraèdres isolés dans la seule solution solide favorise les échanges redox et explique l'augmentation de la sélectivité. Le contact intime entre les deux phases et la formation d'une interface cohérente permet un optimum de rendement en propène du fait de la synergie des propriétés des deux phases. / In order to fill the gap between propene supply and demand, the oxidative dehydrogenation of propane (ODHP) is an alternative solution to the direct dehydrogenation process. Vanadium-modified hydroxyapatites (HAp) are bifunctional catalysts combining acid-base and redox properties which were shown to be of interest for the ODHP reaction. In order to optimize this system, the aim of the work was to investigate the catalytic behavior of the vanadium-modified hydroxyapatites and to establish structure reactivity relationships. By peculiar attention was devoted to the control of synthesis. Provided high pH value is maintained during the synthesis, the Ca10(PO4)6-x(VO4)x(OH)2 solid solution was successfully obtained for x 0→ 6, whereas at lower pH, a mixture of Vx-HAp solid solution and of Ca2V2O7 was obtained from x ≥ 4. For the solid solution, contrary to propene selectivity, the propane conversion does not depend on the vanadium content, unexposed on the surface. The activation of the C-H bond of propane is controlled by an intrinsic properties of the HAp structure, in relation with the thermally activated formation of strong basic O2- anions. Their in situ formation results from the progressive dehydration of OH- columns via an ionic conduction process by protons that is enhanced under catalytic conditions. Due to the tetrameric environment of vanadium in Ca2V2O7 against isolated tetrahedra in the solid solution, redox exchanges are facilitated, improving the selectivity in propene. The intimate contact between the two phases and the formation of a coherent interface leads to an optimal yield in propene, due to synergistic effects of the two phases.