The present work deals with the electrical properties of nanocomposite materials. Samples for the experiment are made of epoxy resin as a matrix and oxides TiO2, Al2O3, WO3, SiO2 as nanofillers in 0.5 and 1 percent performance. The experimental samples are measured in temperature and frequency dependence of relative permittivity, dissipation factor, rezistivity and are broken down by the influence of filler on the electrical properties of the polymer. Attention is also paid to the mechanical properties of nanocomposites.

Les oxydes de métaux de transition lamellaires peuvent servir de catalyseurs pour la conversion de la biomasse, mais leur développement nécessite une meilleure compréhension de leurs propriétés. En conséquence, plusieurs matériaux lamellaires, tels que HNbMoO6, HNbWO6, H2W2O7 et H2WO4, ainsi qu'un nouveau type d'oxydes en couches basés sur Nb et W et caractérisés par des phases d'Aurivillius “en escalier” ont été largement caractérisés notamment par spectroscopie DRX et spectroscopie Raman. La possibilité de convertir les solides précurseurs au lithium ou bismuth en phases protonées a été étudiée. Ces oxydes ont la spécificité d'intercaler des molécules entre les couches, ce qui peut contribuer à l’activité catalytique en phase liquide. Pour identifier les rôles respectifs de l’intercalation et des propriétés de surface comme l’acidité, les matériaux ont été caractérisés en phase liquide par spectroscopie Raman en utilisant des bases organiques telles que les n-alkylamines (butylamine et octylamine) et la pyridine. L'intercalation avec des réactifs possibles, les n-alcools et le 2,5-hexanediol, a également été étudiée. L'activité catalytique de ces oxydes lamellaires a été déterminée grâce à une nouvelle réaction: la cyclo-déshdrataion du 2,5-hexanediol en 2,5-diméthyltétrahydrofurane. HNbMoO6 s’est avéré le catalyseur le plus actif, comparé à des catalyseurs acides conventionnels ou aux autres matériaux lamellaires. L’acidité et la capacité d’intercalation de ces divers matériaux lamellaires ont été comparées pour comprendre les différences observées pour l’activité catalytique. / Layered transition metal oxides have a potential as catalysts for biomass conversions, but their development necessitates a better understanding of their properties. Consequently, several layered materials such as HNbMoO6, HNbWO6, H2W2O7 and H2WO4 as well as new types of layered oxides based on Nb and W and characterized by a “stair-like” Aurivillius phases were extensively characterized notably by XRD and Raman spectroscopy. The possibility to convert the as-synthesised lithium or bismuth precursors to protonated phases was also thoroughly evaluated. Layered oxides have the specificity to intercalate molecules within their interlayer regions, which may be a key feature to catalytic activity for reactions in the liquid phase. In order to evaluate the respective roles of intercalation and surface properties such as acidity, the materials were characterized in the liquid phase by Raman spectroscopy using organic bases such as n-alkylamines (butylamine and octylamine) and pyridine. Intercalation with possible reagents, n-alcohols and 2,5-hexanediol, was also studied. The catalytic activity of these layered oxides was evaluated using a novel test reaction: the cyclo-dehydration of 2,5-hexanediol into 2,5-dimethyltetrahydrofuran. HNbMoO6 proved to be the most active catalyst, compared to conventional acidic catalysts or other layered materials. The acidity and intercalation ability of the various layered materials were compared to understand the differences observed for the catalytic activity.

Les dispositifs électrochromes sont des dispositifs qui permettent de moduler la réflexion ou la transmission de la lumière. Ils recouvrent une grande variété d’applications dans le domaine du visible (vitrages intelligents) et dans le domaine de l’infrarouge (protection thermique des satellites et discrétion optique infrarouge). Les travaux présentés dans ce manuscrit répondent essentiellement à une problématique visant à élaborer un dispositif électrochrome tout solide à émissivité infrarouge variable par un procédé unique de pulvérisation cathodique magnétron. Une nouvelle architecture d’empilement avec une électrode de travail monocouche bi fonctionnelle a été choisie pour réunir les propriétés apportées classiquement par deux couches ou plus sur le haut des empilements électrochromes. Cette nouvelle architecture a nécessité la mise en place d’un procédé de dépôt original de pulvérisation cathodique réactive hydratée. Ce procédé a permis d’obtenir une électrode monocouche à base de trioxyde de tungstène réunissant les propriétés optiques et électroniques souhaitées. Il a également permis de déposer les autres couches de l’empilement, la contre-électrode à base de trioxyde de tungstène et les électrolytes solides conducteurs protoniques à base d’oxyde de tantale ou de zirconium. L’étude de l’ajout d’une couche d’encapsulation à base de dioxyde de cérium a également été menée. Cette architecture a permis d’obtenir un empilement électrochrome tout solide fonctionnel. Ce dispositif complet ainsi élaboré présente de bonnes propriétés optiques dans l’infrarouge en terme de modulation d’émissivité dans les bandes spectrales d’intérêt, à savoir 13 % en bande II et 31 % en bande III. / Electrochromic materials are devices for modulating the reflection or transmission of light. They cover a wide variety of applications in the visible range (smart windows) and the infrared range (thermal protection for satellites and optical infrared discretion). The works presented in this manuscript were essentially responding to the problem of developping an all solid electrochromic device with a variable infrared emissivity by a single process of magnetron sputtering. A new stacking architecture with a working bi functional monolayer electrode was chosen to bring the properties conventionally made by two or more layers on top of electrochromic device. This new architecture has required the establishment of an original deposit process of hydrated reactive sputtering. This process yielded a monolayer electrode based on tungsten trioxide combining the desired optical and electronic properties. It allowed to deposit other layers of the stack, the counter electrode based on tungsten trioxide and the proton conductive solid electrolyte based on tantalum or zirconium oxide. The study of the addition of an encapsulation layer based on cerium dioxide was also conducted. This architecture has resulted in a functional all-solid electrochromic stack. The complete device thus prepared exhibits good optical properties in the infrared emissivity in terms of modulation and in particular in the spectral bands of interest, namely 13 % in MW and 31 % in LW.

Dans les cellules photovoltaïques organiques, le matériau utilisé pour le transport de trous entre la couche active et l'électrode, est généralement un polymère dopé, dont la stabilité peut être problématique. L'objectif de cette thèse a été de développer des matériaux inorganiques, a priori plus stables, pour remplacer les couches de polymères de transport de trous, tout en restant compatible avec les méthodes de dépôts par voie liquide. L'utilisation de nanoparticules dispersées en solution a été choisie car cela permet le dépôt à basse température, sans nécessité de conversion vers une couche fonctionnelle, contrairement aux voies sol-gel. Le premier objectif de ce travail a donc été l'obtention de nanoparticules d'oxyde de tungstène, hydraté ou non, et de thiocyanate de cuivre. Une synthèse de chauffage assisté par micro-ondes a été utilisée pour l'oxyde de tungstène, permettant d'obtenir des nanoparticules de 30 nm et monodisperses. Pour le thiocyanate de cuivre, il a été choisi de travailler par broyage. Les paramètres du broyage ont été optimisés pour obtenir des particules avec la plus faible distribution en taille possible. Le dépôt de ces dispersions de nanoparticules a permis l'obtention de couches minces et la caractérisation de leurs propriétés optoélectroniques, et notamment du travail de sortie, qui s'est révélé adapté pour une utilisation en dispositif. Des cellules solaires organiques de structures standard et inverse incorporant ces matériaux ont ensuite été réalisées. De bonnes performances ont été obtenues avec une couche active à base de P3HT, notamment en structure inverse où la possibilité d'utiliser le thiocyanate de cuivre a été démontrée pour la première fois. Le suivi des performances sous éclairement et atmosphère contrôlée a également été effectué et a montré un vieillissement rapide pour ces cellules comparées aux cellules de référence à couche de transport de trous polymère. / In organic solar cells, a doped polymer is the most used material for hole transport between the active layer and the electrode, but his stability can be an important issue. The goal of this PhD thesis was to develop inorganic materials, expected to be more stable, in order to replace polymer based hole transporting layers. Another requirement was to keep the compatibility with solution-based deposition methods. The target was to develop nanoparticle dispersions, deposited at low temperature and giving directly a functional layer, without the need of further treatments which are usually required via sol-gel processes. A first objective of the present work was thus the elaboration of nanoparticles of tungsten oxide, hydrated or non-hydrated, and copper thiocyanate. A microwave-assisted heating synthesis has been used for tungsten oxide, leading to mono-dispersed particles around 30 nm. Concerning copper thiocyanate, a ball milling technique has been chosen. The process parameters have been optimized to obtain nanoparticles to narrow the size distribution as much as possible. The deposition of the nanoparticles has allowed the formation of thin layers and the characterization of their optoelectronic properties, such as work function, which was shown to be a relevant parameter for a use in devices. Organic solar cells with standard or inverted structures have been fabricated using these materials as a hole transporting layer. Good photovoltaic performances have been obtained, especially in the inverted structure, in which the possibility to use copper thiocyanate has been demonstrated for the first time. Ageing experiments under light in a controlled atmosphere have also been carried out and have shown a rapid drop in performances for these cells compared to cells incorporating polymer based hole transport layers.

The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. / Polymerelektrolytbränslecellen omvandlar den kemiska energin i ett bränsle, exv. vätgas eller metanol, och syrgas  till elektrisk energi. Den höga verkningsgraden samt möjligheten att använda bränsle från förnyelsebara källor gör dem attraktiva som energiomvandlare i framtida hållbara energisystem. En enorm utveckling har skett under det senaste årtiondet men för att kunna introducera polymerelektrolytbränslecellen på marknaden i en större skala måste livstiden öka och kostnaden minska. Elektroderna har en central del i detta då den platina som används som katalysator står för en stor del av kostnaden för bränslecellen. En stor del av prestandaförsämringen med tiden hos bränslecellen kan också relateras till en degradering av den porösa elektroden och en minskad elektrokemiskt aktiv platinayta. I denna avhandling studeras olika bränslecellsreaktioner samt olika katalysatorer och supportmaterial med målet att undersöka möjligheten att förbättra platinakatalysatorns aktivitet, stabilitet och utnyttjandegrad i bränslecellselektroder. Utbytesströmtätheten, i0, för vätgasoxidationen i bränslecell bestämdes till 770 mA cm-2Pt genom försök med modellelektroderna. Denna var högre än vad som framkommit tidigare i litteratur, vilket visar att de kinetiska förlusterna på anoden är mycket små. Katalysatormängden på anoden borde därför kunna minskas utan några större potentialförluster så länge masstransporten av vätgas är tillräcklig. Den elektrokemiskt aktiva ytan, aktiviteten och stabiliteten hos elektroden visade sig kunna påverkas av supportmaterialet. Platina deponerad på volfram oxid hade en högre aktivitet vid höga potentialer vilket relaterades till den förskjutna oxidbildningen på ytan. Elektroder med platina på volframoxid och iridiumoxid var mer stabila än elektroder med platina på kol. Det var även platina på ett icke grafitiserat kol med låg yta jämfört med platina på grafitiserade kol med en hög yta. Platina på metalloxidskikt av volfram och titan visade en högre elektrokemiskt aktiv yta i de cykliska voltamogrammen än platina på kol, vilket förklarades med att båda metalloxiderna har en bra protonledningsförmåga. CO-stripping gav det säkraste måttet på den elektrokemiskt aktiva ytan i en elektrod i bränslecell. CO-stripping visade sig även vara användbart för karaktärisering av degraderingen av en elektrod. Oxidationen av små organiska föreningar påverkades av borttransporten av intermediärer samt av kloridföroreningar. Pt aoch PtRu påverkades olika vilket gjorde det möjligt att få fram information om reaktionsmekanismer och hastighetsbestämmande steg. / QC 20101014

This thesis reports the development of Vanadium Tungsten Oxide (VWO) film as an active detector material for uncooled infrared detectors by using the reactive DC magnetron co-sputtering method. VWO is a doped form of the Vanadium Oxide (VOx) which is known as a prominent material for uncooled infrared detectors with its high TCR, low resistivity, and low noise properties. VOx is a widely preferred material for commercialized uncooled infrared detectors along with its drawbacks. Fabrication is fairly difficult due to its unstable material properties and the need for low process temperatures for a monolithic, CMOS compatible surface micromachining process. Hence, a new material with high performance and easier fabrication is needed. This thesis is the first study at METU on the development of high-performance VWO as an active detector material for uncooled infrared detectors. Deposition studies of VWO primarily started by measuring the effects of deposition parameters upon the magnetron sputtering system. Because the high effectiveness of the tungsten doping has been obtained for the doping level below 10% according to literary information, maximum vanadium (V) deposition rate together with minimum tungsten (W) deposition rate has been initially aimed. TCR of the VWO films has been measured between -2.48 %/K and -3.31 %/K, and the variation of noise corner frequency from 0.6 kHz to 8 kHz has been observed. In addition to these results of VWO, a favorable VOx recipe which has the highest performance done at METU in terms of resistance, TCR, noise and uniformity has also attained during the studies. Structural characterization of VWO is achieved using XPS, XRD, and AFM characterization techniques. Other than the sputtering parameters, post-annealing process and oxygen plasma exposure was examined as well. A general observation of the post-annealing is that it decreases not merely the TCR but also the noise of the deposited film. A short-period oxygen plasma exposure has a constructive effect on the noise behavior. Fabricated vanadium tungsten oxide with sandwich type resistor structure shows very close but better bolometric properties when compared with the yttrium barium copper oxide (YBCO), which is another material being studied in scope of other theses at METU. XPS, XRD and AFM characterization methods have been used for the structural characterization of vanadium-tungsten-oxide.

No description available.

Cette thèse participe à l'étude générale et à la compréhension des relations structure- propriétés optiques de couches minces d'oxyde de tungstène, nanostructurées lors de leur dépôt par la technique Glancing Angle Déposition. Cette technique repose sur le contrôle de l'orientation relative du substrat vis à vis de la source de vapeur.[...] / This thesis contributes to the general study and understanding of the relationship between structure and optical properties of nanostructured tungsten oxide by Glancing Angle Déposition technique. this technique relies on the control of the relative orientation of the substrate to the vapor source.[...]

Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.