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Academic literature on the topic 'Dioxide de niobium'

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Published: 7 July 2024
Last updated: 7 July 2024

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers

Journal articles on the topic "Dioxide de niobium":

1

Sheppard, L. R., A. J. Atanacio, T. Bak, J. Nowotny, M. K. Nowotny, and K. E. Prince. "Niobium diffusion in niobium-doped titanium dioxide." Journal of Solid State Electrochemistry 13, no. 7 (November 6, 2008): 1115–21. http://dx.doi.org/10.1007/s10008-008-0717-x.

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Atanacio, Armand J., Tadeusz Bak, and Janusz Nowotny. "Niobium Segregation in Niobium-Doped Titanium Dioxide (Rutile)." Journal of Physical Chemistry C 118, no. 21 (May 19, 2014): 11174–85. http://dx.doi.org/10.1021/jp4110536.

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Sheppard, L. R. "Niobium Surface Segregation in Polycrystalline Niobium-Doped Titanium Dioxide." Journal of Physical Chemistry C 117, no. 7 (February 7, 2013): 3407–13. http://dx.doi.org/10.1021/jp311392d.

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Song, Li, Alexander Eychmueller, R. J. St. Pierre, and M. A. El-Sayed. "Reaction of carbon dioxide with gaseous niobium and niobium oxide clusters." Journal of Physical Chemistry 93, no. 6 (March 1989): 2485–90. http://dx.doi.org/10.1021/j100343a050.

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Nico, C., M. R. N. Soares, M. Matos, R. Monteiro, M. P. F. Graça, T. Monteiro, F. M. Costa, and M. A. Valente. "Exotic Manganese Dioxide Structures in Niobium Oxides Capacitors." Microscopy and Microanalysis 18, S5 (August 2012): 99–100. http://dx.doi.org/10.1017/s1431927612013153.

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The production of a Tantalum solid electrolytic capacitor requires the impregnation of MnO2 by pyrolysis in one of the several manufacturing steps. It has been reported that niobium oxides are a good alternative, presenting potentially better dielectric properties and a better cost effectiveness. Thus, it is important to study the conditions and the effect of the MnO2 impregnation on niobium oxide in order to understand and optimize the parameters of this process. The morphology and microstructure of the anode is one of the most important aspects that interfere with the dielectric properties of the capacitor. In this work, it is presented a study of the morphology and microstructure of different niobium oxide anodes after electrochemical oxidation (NbO/Nb2O5 core-shell grain structure), and after MnO2 impregnation with different pyrolysis temperatures. This impregnation is made by dipping the anodes, with the NbO/Nb2O5 core-shell structure, in a slurry of Mn(NO3)2. Heating this slurry while the anode is dipped, will lead to a pyrolysis reaction where the liberation of NO2 occurs as a gas, and where the product MnO2 solidifies around the grains.
6

Sievers, M. R., and P. B. Armentrout. "Gas phase activation of carbon dioxide by niobium and niobium monoxide cations." International Journal of Mass Spectrometry 179-180 (November 1998): 103–15. http://dx.doi.org/10.1016/s1387-3806(98)14064-2.

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Cho, Yong Hoon, Soon Ki Jeong, and Yang Soo Kim. "Electrochemical Properties of Chemically Etched-NbO2 as a Negative Electrode Material for Lithium Ion Batteries." Advanced Materials Research 1120-1121 (July 2015): 115–18. http://dx.doi.org/10.4028/www.scientific.net/amr.1120-1121.115.

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The electrochemical properties niobium dioxide (NbO2) was investigated as a negative electrode material for lithium ion batteries. The NbO2electrode showed a large irreversible capacity and small discharge capacity. The results of X-ray photoelectron spectroscopy indicate that the poor electrode performance of NbO2may be caused by niobium pentoxide (Nb2O5) formed on the surface of active material. The Nb2O5could be removed by chemical etching to some extent, thus improving the electrode performance.
8

Muhammad Hussian, Hasan Mahmood, Muhammad Abdullah, Sikandar Raza,. "Computing Topological Indices for Niobium Dioxide and Metal-Organic Frameworks via M-Polynomials." Power System Technology 48, no. 1 (April 8, 2024): 211–27. http://dx.doi.org/10.52783/pst.268.

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This paper investigates the topological properties of metal-organic frameworks and niobium dioxide using M-polynomials. The stability and wide range of bonding that the molecule exhibits make it a promising candidate for a number of uses, such as energy storage, gas detection, and catalysis. We use M-polynomials to calculate several degree-based topological indices for metal-organic frameworks and niobium dioxide. The M-polynomial is one such fundamental polynomial that provides a way to derive a multitude of degree-based topological indices. These indices are crucial for research in chemistry, biology, and physics and are derived from degree-based M-polynomials. This work develops a new M-polynomial algorithm for the computation and comparison of several degree-based molecular descriptors.
9

Gautam, Subodh K., Arkaprava Das, S. Ojha, D. K. Shukla, D. M. Phase, and Fouran Singh. "Electronic structure modification and Fermi level shifting in niobium-doped anatase titanium dioxide thin films: a comparative study of NEXAFS, work function and stiffening of phonons." Physical Chemistry Chemical Physics 18, no. 5 (2016): 3618–27. http://dx.doi.org/10.1039/c5cp07287e.

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Alharthi, F. A., F. Cheng, E. Verrelli, N. T. Kemp, A. F. Lee, M. A. Isaacs, M. O’Neill, and S. M. Kelly. "Solution-processable, niobium-doped titanium oxide nanorods for application in low-voltage, large-area electronic devices." Journal of Materials Chemistry C 6, no. 5 (2018): 1038–47. http://dx.doi.org/10.1039/c7tc04197g.

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Synthesis and characterization of surface-stabilised, niobium-doped titanium dioxide (Ni-TiO2) nanorods in a simple one-step reaction using oleic acid as both a stabilizer and solubilizing agent.
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Journal articles Dissertations / Theses

Dissertations / Theses on the topic "Dioxide de niobium":

1

Fakih, Ali. "Current controlled negative differential resistance in niobium dioxide." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS099.

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Le dioxyde de niobium (NbO2) a récemment suscité un vif intérêt dans les domaines de la physique des solides et nano-dispositifs technologiques. D'une part, le NbO2 isolant à température ambiante subit une distorsion structurelle accompagnée d'une transition de phase électronique par laquelle il devient métallique à des températures supérieures à 1080 K. D'autre part, NbO2 présente une phase de résistance différentielle négative sous l'application du courant électrique, un phénomène connu sous le nom de résistance différentielle négative contrôlée par le courant CC-NDR. Dans cette thèse, nous avons fabriqué des films minces de NbO2 par la technique de pulvérisation RF-mangnétron sur des substrats amorphes et cristallins (verre et silicium). Les films déposés sont toujours amorphe, et un traitement de recuit des films déposés est nécessaire pour atteindre la cristallinité. Lors des études électroniques sur NbO2, nous avons observé la CC-NDR avec une hystérèse dans les courbes V(I). Nous avons montré que cette hystérèse dynamique est due à l'inhomogénéité de la température. Les mesures de transport électronique en fonction de la température montrent qu'il n'y a pas de transition métal-isolant associée à la CC-NDR. Par ailleurs, nous avons montré qu’il y avait un changement similaire de la conductivité lié à la température dans les échantillons amorphes et cristallins, cependant, l'échantillon amorphe est un meilleur conducteur électronique et thermique. Enfin, nous avons prouvé que la CC-NDR peut être simplement expliqué par la création de porteurs excités thermiquement dans un semi-conducteur, sans la nécessité de faire appel à des mécanismes de transport plus complexes
Niobium dioxide (NbO2) has been recently gaining a lot of interest in the fields of solid state physics and technological nano-devices. On one hand, NbO2 undergoes a structural distortion accompanied by an electronic phase transition where the material changes from an insulating state at room temperature into a metallic state at temperatures above ∼ 1080 K. On the other hand, NbO2 exhibits a negative differential resistance phase under the application of electric current, a phenomenon known as current-controlled negative differential resistance CC-NDR. In this thesis, we have fabricated thin films of NbO2 by RF-mangentron sputtering technique on amorphous and crystalline substrates (glass and silicon). The deposited films were always amorphous, and annealing treatment of the as-deposited films was necessary to achieve crystallinity. . Upon performing electronic studies on NbO2, we witnessed CC-NDR with a hysteresis in the V(I) curves. We showed that hysteresis in CC-NDR is due to temperature inhomogeneity. Simultaneous electronic transport and Raman measurements show that CC-NDR is not associated to a phase transition. Moreover, we showed that there is a similar temperature driven change in conductivity in both the amorphous and the crystalline samples, however, the amorphous sample is a better electronic and thermal conductor. Finally, we proved that the CC-NDR may be simplyexplained by the creation of carriers by temperature in a semiconductor, without the need for invoking more complicated transport mechanisms
2

Song, Inho. "Defect structure and DC electrical conductivity of titanium dioxide-niobium dioxide solid solution." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054571769.

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3

Snook, M. W. G. "The preparation and optical properties of niobium dioxide films." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374936.

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Niobium dioxide films have been prepared by the radio frequency sputtering of Niobium dioxide powder targets. Polycrystalline films have been deposited onto Silicon substrates maintained at temperatures exceeding 900 K during preparation. Characterisation by X-ray diffraction and E.S.C.A. indicates that the Argon environment during sputtering must be doped with approximately 500 to 1000 ppm of Hydrogen for the growth of Niobium dioxide films. Optical measurements were carried out on single crystals and thin films of Niobium dioxide as well as Vanadium dioxide films. The optical measurements were carried out over a wavelength range of 0.5 to 15 um for Niobium dioxide and 0.5 to 6 um for Vanadium dioxide. The temperature range over which measurements were made on Niobium dioxide (in a vacuum) was from 90 to 1200 K and for Vanadium dioxide from 300 to 370 K. The optical properties (refractive index and extinction coefficient) of Niobium dioxide and Vanadium dioxide were calculated across both of their respective thermally excited transitions. It was found that there was an abrupt change in the optical properties of both Niobium dioxide and Vanadium dioxide at their respective transition temperatures.
4

Sanghera, J. S. "Electrical properties of aluminosilicate glazes containing niobium doped titanium dioxide." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37846.

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Sirjita, Eduard-Nicolae. "Elaboration and correlation of structure/optical and electrical properties of phase transition oxide materials (VO2, W-doped VO2 and NbO2)." Electronic Thesis or Diss., Limoges, 2024. https://aurore.unilim.fr/theses/nxfile/default/cfd27744-856a-4645-a183-cbf2ff31ef34/blobholder:0/2024LIMO0005.pdf.

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Cette thèse vise la réalisation et la caractérisation structurale, optique et électrique de couches minces de matériaux oxydes ayant des propriétés de transition isolant-métal (MIT), plus particulièrement des oxydes de vanadium (VO2 et VO2 dopé avec W) et du dioxyde de niobium (NbO2). Le dépôt de ces couches minces a été effectué par pulvérisation magnétron réactive dans une atmosphère Ar/ O2. Le processus d'optimisation des films minces a permis d'obtenir des informations précieuses sur les effets du processus de fabrication sur les caractéristiques structurelles, optiques et électriques. En outre, les films ont été intégrés dans divers dispositifs tels que des modulateurs THz activés thermiquement/électriquement, des métacanvases reconfigurables optiquement et des dispositifs oscillants. Les informations fournies dans ce manuscrit sont d'un grand intérêt pour l'intégration de films de VO2 et de VO2 dopé avec W dans des dispositifs pouvant fonctionner dans différents domaines. Ce travail permet également d'approfondir notre compréhension des films de NbO2, un domaine relativement moins étudié mais particulièrement intéressant pour les applications nécessitant une plus grande stabilité à la température
This thesis aims at the realization and structural, optical, and electrical characterization of thin films of oxide materials with insulator-to-metal transition (MIT) properties, more specifically vanadium oxides (VO2 and W-doped VO2) and niobium dioxide (NbO2). The deposition of these thin films was performed using reactive magnetron sputtering in an Ar/ O2 atmosphere. During the optimization process of the thin films, valuable insights were gained into the effects the fabrication process has over the structural, optical and electrical characteristics. Furthermore, the films were integrated into various devices such as thermally/ electrically activated THz modulators, optically reconfigurable metacanvases and oscillating devices. The information provided in this manuscript is of high interest for the integration of VO2 and W-doped VO2 films into devices that can operate in various fields. This work also deepens our understanding of NbO2 films, an area with comparatively less research but of particular interest for applications requiring higher temperature stability
6

Duncan, Morris. "Surface and sensor studies of doped titanium dioxide." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365772.

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Modingwane, Boitshoko Goitseone. "Investigation of Pt supported on carbon, ZrO2, Ta2O5 and Nb2O5 as electrocatalysts for the electro–oxidation of SO2 / Boitshoko Goitseone Modingwane." Thesis, North-West University, 2011. http://hdl.handle.net/10394/5557.

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The gradual depletion of and dependence on fossil fuels, air pollution and global warming have all accelerated the development of alternative energy systems which use hydrogen as an energy carrier. The hybrid sulphur cycle (HyS) is the foremost electrothermochemical process that can produce hydrogen as the energy carrier. The HyS cycle consists of two units, namely the sulphuric acid decomposition reactor and the sulphur dioxide electrolyser (SDE). The SDE is responsible for the SO2 electrooxidation to sulphuric acid and protons at the anode and the electro–reduction of protons to hydrogen at the cathode. This research study focuses on the kinetic data collected from the prepared catalysts for SO2 electro–oxidation at the anode. Platinum dispersed on carbon, niobium pentoxide, tantalum pentoxide and zirconium dioxide as electrocatalysts were prepared using sodium borohydride as a reducing agent. These electrocatalysts were characterized using transmission electron microscopy and x–ray diffraction. Cyclic voltammetry was used to study the electrochemical active surface area (EAS) and the results showed that Pt/ZrO2–C had a higher EAS area than Pt/Ta2O5–C, Pt/Nb2O5–C and Pt/C. The high EAS of Pt/ZrO2–C can be explained by the low crystal size however after a series of linear polarisation scans Pt/ZrO2–C experiences a much greater area loss than all the other catalysts. Linear polarisation scans for each of the catalysts revealed that the influence of increased temperature and sulphuric acid concentration were showed improved results. Levich and Koutecky–Levich plots revealed that the SO2 oxidation is a multistep reaction on all the prepared catalysts and that there are regions which are kinetic and diffusion controlled and diffusion–only controlled. Pt/Ta2O5–C catalysts exhibited superior catalytic activity and stability compared Pt/Nb2O5–C, Pt/ZrO2–C and Pt/C. The Pt/ZrO2–C exhibited the most inferior catalytic activity and stability.
Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.
8

Stöver, Julian. "Defect related transport mechanism in the resistive switching materials SrTiO3 and NbO2." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23122.

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Diese Arbeit beschäftigt sich mit den elektrischen Eigenschaften der resistiven Schaltmaterialien SrTiO3 und NbO2. Im ersten Teil werden NbO2 (001)-Dünnschichten untersucht. Bisher sind die für NbO2-Dünnschichten in der isolierenden Phase gemessenen spezifische Widerstände um einen Faktor von 200 niedriger als der in NbO2-Einkristallen gemessene 10 kΩ cm Widerstand. In dieser Arbeit wird der spezifische Widerstand von NbO2-Dünnschichten auf 945 Ω cm erhöht. Es wird gezeigt, dass leitfähige Perkolationspfade entlang der Korngrenzen für die Abnahme des spezifischen Widerstandes verantwortlich sind. Durch temperaturabhängige Leitfähigkeitsmessungen wurden Defektzustände identifiziert, die für die Verringerung des spezifischen Widerstandes gegenüber dem theoretischen Wert verantwortlich sind. Im zweiten Teil wird der Einfluss des Ti-Antisite Defekts auf das resistive Schalten in SrTiO3 Dünnschichten untersucht, welche mit metallorganischer Dampfphasenepitaxie gezüchtet wurden. Dabei werden sowohl stoichiometrische als auch Strontium defizitäre Schichten untersucht. Es wird über temperaturabhängige Permittivitätsmessungen gezeigt, dass durch Kristalldefekte die weiche Phononenmode gestört wird und bei stark strontiumverarmten Schichten polare Nanoregionen gebildet werden, was auf die Bildung des TiSr Defekts zurückgeführt wurde. Darüber hinaus wird gezeigt, dass stark strontiumdefiziente SrTiO3 -Schichten ein stabiles resistives Schalten mit einem Ein-Aus-Verhältnis von 2e7 bei 10 K aufweisen, während stöchiometrische Dünnschichten kein stabiles Schalten zeigen. Es wird ein diodenartiger Transportmechanismus, der im hochohmigen Zustand auf Schottkyemission beruht und ihm niederohmigen Zustand durch defektassistierten Tunnelstrom dominiert wird, identifiziert. Daraus wurde ein neues Modell für das resistive Schalten, basierend auf dem TiSr Defekt und der induzierten Ferroelektrizität, entwickelt.
In this work, the impact of crystal defects on the resistive switching materials SrTiO3 and NbO2 is investigated. The work is divided into two parts. In the first part, NbO2 (001) thin films are studied. So far, resistivities measured for NbO2 thin films in the insulating phase are by a factor of 200 lower than the 10 kΩ cm resistivity measured in NbO2 single crystals. To make this material applicable for resistive switching, the resistivity in the insulating phase has to be increased to effectively block the current in the high resistive state. Throughout the investigations presented in this work, the resistivity of NbO2 thin films is increased to 945 Ω cm. It is shown that conductive percolation paths along the grain boundaries are responsible for the decrease in resistivity. Temperature-dependent conductivity measurements identified defect states responsible for the reduction in resistivity from the theoretical value. In the second part of this work, the influence of the Ti anti-site defect on resistive switching in SrTiO3 thin films grown by metal-organic vapor phase epitaxy is studied. Both stoichiometric and strontium deficient thin films are studied. It is shown via temperature-dependent permittivity measurements that crystal defects harden the soft phonon mode and polar nano regions are formed in highly strontium deficient films, which was attributed to the formation of Ti antisite defects. In addition, highly strontium deficient SrTiO3 films are shown to exhibit stable resistive switching with an on-off ratio of 2e7 at 10 K, whereas stoichiometric thin-films do not show stable switching. A diode-like transport mechanism based on Schottky emission in the high-resistance state and dominated by defect-assisted tunneling current in the low-resistance state is identified. From this, a new model for resistive switching based on the Ti antisite defect and the induced ferroelectricity is developed.
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Khair, Mira. "Oxydo-réduction et spéciation des produits de fission corrosifs dans les combustibles oxydes : évaluation des bénéfices d'un combustible tamponné en pO2." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0360.

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L’amélioration des performances du combustible nucléaire nécessite, aussi bien en régime nominal que lors de rampes de puissance ou de transitoires accidentels, d’être en mesure de maîtriser les effets délétères induits par la réactivité chimique des produits corrosifs (générés par la fission) susceptibles de provoquer des ruptures de gaine. Dans cet objectif, ce travail vise à maîtriser le potentiel d'oxygène de fonctionnement du combustible dans un domaine stabilisant les formes non corrosives de l’iode, par l’usage in-situ de systèmes tampons d’oxydo-réduction appropriés. En fonctionnement nominal, le potentiel en oxygène est assez proche de celui imposé par le tampon (MoO2/Mo). Par conséquent, le premier objectif de ce travail a été de clarifier la thermochimie (solubilité et spéciation dans UO2) du couple (MoO2/Mo). Nous avons étudié la transition MoO2 ⇌ Mo dans UO2 en fonction de la pO2 et de la température, par spectroscopie d'absorption des rayons X (XAS) in situ au synchrotron KARA (Allemagne). Nous montrons que les réactions d’oxydation du molybdène sont toujours possibles thermodynamiquement, quelles que soient les conditions de température mais avec une cinétique lente à 800°C. La vitesse d’oxydation augmente avec la température. De plus, la solubilité de Mo dans UO2 a été mesurée par SIMS (spectrométrie de masse des ions secondaires) et EPMA (microsonde électronique). Nous proposons une limite de solubilité de l’ordre de10-4 mol Mo/mol U, soit 0,01 % m de Mo/UO2. Ensuite, le niobium, sous ses formes redox Nb2O5/NbO2, a été identifié comme un candidat prometteur de par ses propriétés physico-chimiques et neutroniques. La première étape a consisté à préparer des céramiques UO2 contenant le couple tampon redox. Un procédé de fabrication spécifique du combustible UO2 tamponné, dopé par le couple (Nb2O5/NbO2), a été développé afin de préserver les deux formes oxydo-réductrices du tampon oxygène dans les pastilles lors du frittage.Ce processus a été également validé pour UO2 dopé par le couple (MoO2/Mo). Nous avons aussi montré quel e tampon (Nb2O5/NbO2) introduit initialement se transformait lors du frittage en (UNb2O7/NbO2),présentant un équilibre très proche de celui du tampon initial et donc apte à remplir le rôle de tampon depO2 dans le domaine visé. Ensuite, l’objectif final a été la validation de l’effet tampon lié à l’ajout du couple(Nb2O5/NbO2) dans UO2. Nous avons donc d’abord étudié par diffraction des rayons X à haute résolution et haute température (HR HT XRD) et par diffraction des neutrons (DN) la variation du paramètre de maille de la matrice UO2 fluorite en présence du couple oxydo-réducteur qui va agir comme un tampon local pour stabiliser la pO2 au sein du système et la stœchiométrie de la matrice UO2+x. Nous montrons également que le système U-Nb-O présente de nombreuses phases ternaires incluant les états d'oxydation Nb4+ etNb5+, toutes stables sur un domaine étroit de pO2. Ainsi, ces différentes phases ternaires participent à des systèmes tampons, qui permettent de réguler les perturbations oxydo-réductrices pouvant être imposées au matériau sans modification notable de la stœchiométrie du combustible (stabilité du paramètre de maille). Ensuite, les pastilles UO2 élaborées avec le couple tampon Nb2O5/NbO2 ont été implantées avec des ions césium, iode, molybdène et tellure dans une couche superficielle (environ 1 μm). La spéciation de ces espèces a été caractérisée par spectroscopie d'absorption des rayons X (synchrotron KARA)
Improvement of nuclear fuel performances requires reducing the stability of corrosion fission gas, in particular the speciation of potentially corrosive fission products (Cs, I, Te). Doping uranium dioxide with an oxydo-redox buffer couple is the improvement axis considered in this work. It aims at improving redox buffer couple effect on pO2 (oxygen partial pressure) and their impact on properties of speciation of fission products in UO2. Actually, in typical nominal operation, the oxygen potential is quite close to that imposed by the (Mo/MoO2) buffer. The first objective of this work was to clarify the thermochemistry (solubility and speciation in UO2) of the (Mo/MoO2) couple. We studied the MoO2 ⇌ Mo transition in UO2 as a function of pO2 and temperature by X-ray Absorption Spectroscopy (XAS) in situ at the KARA synchrotron (Germany). We show that the oxidation reactions of molybdenum are always thermodynamically possible, whatever the temperature conditions but with a slow kinetics at 800°C. The oxidation rate increases with temperature. In addition, the solubility of Mo in UO2 was measured by SIMS (Secondary Ion Mass Spectrometry) and EPMA (Electron probe micro-analyzer). We found a solubility limit of the order of 10-4 mol Mo/mol U, i.e. 0.01 %weight of Mo/UO2.Then niobium, with its redox forms Nb2O5/NbO2, has been identified as a promising candidate due to different selection criteria (physico-chemical and neutronic properties). The first step was to prepare UO2 with this buffer. A specific manufacturing process of the buffered UO2 fuel, doped with the (Nb2O5/NbO2) couple has been developed in order to preserve both oxido-reducing forms of the oxygen buffer in the pellets while sintering. This process has been also validated for UO2 doped with the (MoO2/Mo) couple. We have shown that the initially introduced (Nb2O5/NbO2) buffer was transformed during sintering into (UNb2O7/NbO2). The equilibrium of the latter couple is very close to that of the initial buffer and therefore it can fulfill its role of pO2 control in the targeted domain.Then, the final objective was the validation of the buffer effect related to the addition of (Nb2O5/NbO2) in UO2. So we first studied by means of High Resolution X-Ray diffraction at high temperature (HR HT XRD) and Neutron Diffraction (DN) the variation of the lattice parameter of the UO2 fluorite matrix in presence of the niobium pO2 buffer. The latter can act as a local buffer enforcing a stabilization of the pO2 within the system and therefore of the stoichiometry of the UO2+x matrix. We also show that the U-Nb-O system has many ternary phases including Nb4+ and Nb5+cations, all stable on a narrow domain of pO2. Thus, these different ternary phases participate to buffer systems, which make it possible to regulate the oxido-reducing disturbances imposed on the material without any notable modification of the pO2 (stabilization of the lattice parameter).Then, the UO2 pellets elaborated with the (Nb2O5/NbO2) buffer couple were implanted with cesium, iodine, molybdenum and tellurium ions in a thin surface layer (1 µm approximately). Speciation were characterized by X-Ray Absorption Spectroscopy, using synchrotron radiation (KARA)
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LORENZI, ROBERTO. "Silica based functional materials: - Charge transport in nanostructured SnO2: SiO2 thin films. - Second harmonic generation in niobium potassium silicate glasses. - Tapered silica optical microfibres for gas sensors." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10933.

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"Charge transport in nanostructured SnO2:SiO2 thin films": Silica based nanostructured thin films grown on silicon substrates are promising materials for novel light emitter devices. In particular, tin dioxide is a wide band gap n-type semiconductor (Eg=3.6 eV) with an expected band-to-band emission centered in the ultraviolet (344 nm) region of the electromagnetic spectrum. Our group succesfully demonstrated UV emission from such systems, but at the beginning of my work many issues in charge transport processes needed to be explained. Aim of this project was to clarify electric transport and charge trapping mechanisms. As a result of a materials science approach we can now interpret the experimental data through specific relationships between synthesis conditions, clustering morphology (nanoparticle (NP) size distribution and volumic concetration, interphase substoichiometry, film thickness), and electric response. The observed phenomena have been analyzed within the percolation theory. Main results concern: electric transport of both holes and electrons is sustained by NP-to-NP hopping events and dielectric enhancement results from oscillating charges (holes) on NPs. "Second Harmonic Generation in potassium niobium silicate glasses": Second harmonic generation (SHG) is a non linear optical process largely employed in current laser technology and photonics. However in almost every application the material employed for these purposes are single crystals. Therefore the possibility to achieve large SHG in amorphous systems may lead to devices with innovative configurations. SHG may occur only if the system is non-centrosymmetric, therefore for glasses it is forbidden due to intrinsic isotropy. The inversion symmetry can be broken up with poling treatments. They consist in applying strong electrostatic field while the sample is stressed by external perturbation (typically heat, electron beam or laser light). We have explored the effect of thermal poling treatment on potassium niobium silicate glasses on inducing non linear optical properties. The results have revealed a strong SHG associated with structural modifications. The proposed mechanism involves a rearrangement of niobium oxide groups mediated by non bridging oxygen and potassium ion transport across the glass. These new charge arrangements form a non-centrosymmetric region underneath the anodic contact responsible of the detected SH signal. "Tapered silica optical microfibres for gas sensors": In the last years, tapered silica fibres have attracted much interest in photonic research, because of peculiar properties emerging in waveguides with lateral dimensions of the same order of the guided modes. In particular, in these structures the large evanescent field enables some interesting properties, such as microfluidic sensors and high Q optical resonators (coiling the tapered fibre), non-linear effects and supercontinuum generation. In this project, carried out at the University of Southampton (UK) in the group of Dr. Gilberto Brambilla, we have explored the feasibility of an innovative optical absorption device, based on ring down spectroscopy. In this case we are interested in a sensor for in-line application: a fluidic channel wrapped with tapered fibre in which the analyte can flow. The large power fraction outside the fibre interacts with the flowing medium and any change in the surrounding optical properties (refractive index or absorption coefficient) leads to a modification of the recorded light intensity propagating in the fibre. The idea is to exploit ring down time of a silica tapered microcoil resonator as an indicator of the absorption coefficient of a gas (or a liquid) flowing in the channel.
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Books on the topic "Dioxide de niobium":

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Snook, Michael William George. The preparation and optical properties of niobium dioxide films: ... and comparison... with Nb02 singlecrystals and V02 films. Bradford, 1986.

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Book chapters on the topic "Dioxide de niobium":

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R., Deeksha, and Deepak Kumar. "Design of Supported Catalysts for Nitrogen Reduction Reaction: A Continuous Challenge." In Advanced Materials and Nano Systems: Theory and Experiment (Part-1), 66–91. BENTHAM SCIENCE PUBLISHERS, 2022. http://dx.doi.org/10.2174/9789815050745122010007.

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The production of ammonia is facilitated by the nitrogen reduction reaction (NRR), where the inert di-nitrogen molecule is converted to ammonia. Along with being a major carrier of hydrogen, ammonia holds authority in the fertilizer realm. Therefore, it is inevitable to develop a viable and eco-friendly method of production that is cost-effective and resource-efficient. The primary challenge of nitrogen reduction is the cleavage of the particularly stable nitrogen bond. The most popular Haber-Bosch process for ammonia production, although efficient, is highly energy-intensive, and the need for maintaining exceptionally high temperature and pressure conditions is an environmental concern. As an alternative, the direct conversion of nitrogen has been carried out by photocatalysis and electrocatalysis. However, this strategy falls short of achieving superior conversion efficiencies. Consequently, it is conceivable that a fitting catalyst can be the solution for the difficulties associated with NRR. Over the years, several attempts have been made at formulating the best catalyst, including chromium oxynitride nanoparticles, niobium dioxide, various metal (Ru, Al, Rh, Ga) clusters, single-atom catalysts supported on different surfaces, and double atom catalysts. Recently, perovskites have emerged into the spotlight as excellent catalysts for NRR. In this chapter, we discuss the challenges faced by researchers to formulate righteous catalysts for the sustainable reduction of nitrogen by studying each of these types with a few examples. We also review the recent advancements in the experimental domain of NRR using different electrochemical cells.

Conference papers on the topic "Dioxide de niobium":

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Sheppard, L. R., A. Atanacio, T. Bak, J. Nowotny, and K. E. Prince. "Effect of niobium segregation on surface properties of titanium dioxide." In SPIE Optics + Photonics, edited by Lionel Vayssieres. SPIE, 2006. http://dx.doi.org/10.1117/12.674547.

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Vogel, Ralf, and Horst Weller. "Sensitization of titanium dioxide and niobium pentoxide electrodes by strongly quantized semiconductor particles." In Optical Materials Technology for Energy Efficiency and Solar Energy, edited by Anne Hugot-Le Goff, Claes-Goeran Granqvist, and Carl M. Lampert. SPIE, 1992. http://dx.doi.org/10.1117/12.130575.

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Ribeiro, Joana M. "Transparent Niobium-Doped Titanium Dioxide Thin Films with High Seebeck Coefficient for Thermoelectric Applications." In 64th Society of Vacuum Coaters Annual Technical Conference. Society of Vacuum Coaters, 2021. http://dx.doi.org/10.14332/svc21.proc.0019.

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Kao, M. C., H. Z. Chen, S. L. Young, B. Ni Chuang, W. W. Jiang, and J. S. Song. "The structure and optical properties of sol-gel derived transparent titanium dioxide thin films doped with niobium." In 2011 IEEE 4th International Nanoelectronics Conference (INEC). IEEE, 2011. http://dx.doi.org/10.1109/inec.2011.5991730.

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Chen, Hsi-Chao, Yu-Hung Yen, Ya-Jun Zheng, Jhe-Ming Chang, Yu-Ren Zhao, and Tan-Fu Liu. "Investigation of Optoelectronic and Band-gap of Niobium Doped Titanium Dioxide Film Deposited by Electron-beam Evaporation with Ion-beam Assisted." In Novel Optical Materials and Applications. Washington, D.C.: OSA, 2020. http://dx.doi.org/10.1364/noma.2020.jtu4c.3.

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