Tesis sobre el tema "Isolants Mott – Propriétés électriques"
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Koussir, Houda. "Multiscale study of the electric field induced transition in the Mott phase of GaMo4S8 crystals and TaSe2 monolayers". Electronic Thesis or Diss., Université de Lille (2022-....), 2024. http://www.theses.fr/2024ULILN004.
Texto completoIn the realm of condensed matter physics, Mott insulators are essential for exploring complex electronic phenomena, with significant implications for high-temperature superconductivity and quantum spin liquids. This thesis investigates two types of such materials, distinguished by their dimensionality : GaMo4S8 crystals and monolayer 1T-TaSe2.After presenting their properties in the first chapter, the second chapter addresses the local-scale characterization techniques used to characterize both materials, namely scanning tunneling microscopy and spectroscopy for structural and electronic studies, and multi-tip scanning tunneling microscopy for transport measurements. The latter technique was particularly employed to analyze transport in GaMo4S8. The study then delved into the material response to external electric fields, examining the threshold electric field in relation to the electrode geometry and exploring the temporal evolution of switching times in connection with inter-electrode distances. The achievement of volatile transitions opens prospects for applications such as the operation of a microneuron at room temperature.To enhance the control over phase transition properties of Mott insulators, it is beneficial to consider two-dimensional systems where the current flow is restricted within the crystal plane. The final chapter focuses on the 1T phase of TaSe2, epitaxially grown on gallium phosphide (GaP) semiconductor substrates. Low-temperature scanning tunneling microscopy studies reveal that 1T-TaSe2 monolayers exhibit not only the characteristic charge density modulation (Star of David) of the charge density wave phase but also a unique Moiré pattern due to the monolayer interaction with the GaP substrate. Scanning tunneling spectroscopy has identified a bandgap, hallmark of the Mott insulating state. This state is further substantiated by temperature-dependent transport measurements that show the persistence of the insulating phase up to 400 kelvins. Notably, spectroscopic measurements with varying tip-to-surface distances have unveiled insulator to metal transitions at low temperatures. The observation of such transitions suggests that this large-scale heterostructure could be a material of choice for neuromorphic applications
Amsalem, Patrick. "Etude spectroscopique de films de phtalocyanines adsorbés sur surfaces métalliques". Aix-Marseille 1, 2008. http://www.theses.fr/2008AIX11082.
Texto completoThe initial steps of the interface formation between metallo-phthalocyanines (ZnPc et ZnPcCl8) and Ag(111) or Ag(110) surfaces have been studied by Scanning tunnelling microscopy, Low-energy electron diffraction, Photoelectron spectroscopy and High-resolution electron energy loss spectroscopy. On both surfaces, the molecular self-assembly leads to the formation of long range ordered monolayers at room temperature. For each system, upon adsorption, the molecules are significantly distorted and charge transfers from the surface to molecules are detected. The resulting doped monolayers are found metallic or insulating, depending on the structural details of the molecular networks. This link between structural and electronic properties is rationalized in terms of electronic correlations. Consequently, the monolayers that retain insulating properties upon electronic doping can be described in terms of Mott-Hubbard insulator. Such results provide new insights for the understanding of the fundamental phenomena at organic/metal interfaces and are susceptible to be extended to other organics adsorbed on solid surfaces
Guiot, Vincent. "Comportement hors équilibre des isolants de Mott sous champ électrique : transition résistive par effet d'avalanche électronique dans les composés AM4X8 (A=GA, Ge ; M=V,Nb,Ta;X=S,Se) et Ni (S, Se)2". Nantes, 2011. http://www.theses.fr/2011NANT2119.
Texto completoDuring the last quarter of century, major breakthroughs in Solid State Physics (superconductivity, magnetoresistance) occurred in the vicinity of the Mott metal-insulator transition (MIT). This transition is due to electronic correlations and is usually controlled by electronic doping and by pressure. Despite its high applicative potential, control of the MIT by electric field still remains less studied. Recently, a peculiar electric pulse induced resistive switching (EPIRS) was discovered in the family of correlated compounds AM 4 X 8 (A= Ga, Ge; M= V, Nb, Ta; X= S, Se). In this PhD thesis, the Mott insulating electronic state of these compounds is firstly investigated. We show then that electric fields above threshold values E,h as low as I kV/cm allow to break the Mott insulating state of these materials. This phenomenon appears to be of purely electronic origin and can be pinned to cause a non volatile transition. A study of the new solid solution GaTa4(Se,Te)s, developed on purpose, demonstrates the E,h dependence with the Mott gap. Comparison with conventional semiconductors behaviour under electric field strongly suggests that this transition corresponds to an electronic avalanche, in contrast with theoretical predictions of a Zener effect. Peculiar dynamics of transition and strong electro-mechanical coupling experimentally observed are suggested to originate from the Mott insulating state of the compounds. A similar study of the Ni(S,Se)2 solid solution and of the organic compound K-(BEDT-TTF)2Cu[N(CN) 2 ]Cl confirms the generalization of this electronic avalanche effect to other Mott insulators
Haas, Vincent. "Caractérisation 3D des charges électriques dans les isolants polymères minces par imagerie thermoacoustique". Toulouse 3, 1997. http://www.theses.fr/1997TOU30169.
Texto completoTran, Duy Chau. "Propriétés diélectriques de liquides isolants d'origine végétale pour applications en haute tension". Grenoble 1, 2009. http://www.theses.fr/2009GRE10017.
Texto completoFor the environmental, economic or technical reasons, oils based on natural esters were used to replace mineral oil in electrical equipments in low and medium voltage. This work consists on characterization of a mixture (RS50) of low viscosity natural esters based on rapeseed oil for applications in high voltage transformers. The influence of humidity, temperature, particle content and thermal aging on its dielectric properties such as permittivity, conductivity, losses and electrical strength was highlighted. The RS50 has a high-water solubility, its conductivity, permittivity and losses are both higher than those of mineral oil but these differences are reduced in aged oils. Its electrical strength is similar to mineral oil even after aging. However, an analysis more precise of prebreak down and breakdown phenomena in specific configurations have shown that natural esters are less favorable for high voltage applications than mineral oil. In parallel, a methodological study was carried out. Advantage of using the frequency spectroscopy measuring method for the characterization of insulating liquids is highlighted. The validity of conditions for the dielectric strength measurement in the liquid insulation, which is traditionally imposed following the standards, was also discussed
Hadid, Mohammed Abderahmane. "Conception d'un dispositif de mesure des charges injectées dans les polymères sous champ alternatif divergent : application au vieillissement électrique". Toulouse 3, 1992. http://www.theses.fr/1992TOU30249.
Texto completoChailan, Jean-François. "Contribution des spectrométries mécanique et diélectrique à l'étude du vieillissement d'élastomères en ambiance nucléaire". Lyon 1, 1993. http://www.theses.fr/1993LYO10236.
Texto completoGuerret-Piecourt, Christelle. "Effets de la génération, de l'injection et du piégeage des charges électriques sur les propriétés des isolants". Habilitation à diriger des recherches, Ecole Centrale de Lyon, 2005. http://tel.archives-ouvertes.fr/tel-00128125.
Texto completoDubost, Vincent. "Étude par microscopie/spectroscopie tunnel de la transition isolant/métal induite par pulses électriques dans GaTa4Se8". Paris 6, 2009. http://www.theses.fr/2009PA066633.
Texto completoIn this PhD thesis, we have studied using scannng tunneling microscopy/spectroscopy the two main phenomena due to interactions between electrons : superconductivity and Mott Metal-Insulator transition. The study of the intercalated graphite CaC6 show that this superconductor is well described by conventionnal BCS theory with a zero temperature gap of 1. 6 +/-0. 2 meV, even if a small spectroscopic broadening suggest a weak anisotropy in the ab plane. The imaging of vortex lattice give for the coherence length extrapolated at zero temperature 38 nanometers. The main part of the manuscript is dedicated to the study of the Electric Pusle Insulator-Metal Transition in the weak Mott Insulator GaTa4Se8. The application of the electric pulse induces the formation of metallic zones in a insulating matrix in the bulk material. These observations provides a natural explanation for the phenomenological model used in transport measurements. The application of voltage sweeps during spectroscopic measurements trigger a local Insulator-Metal transition and for increased biases (V>1. 0V), one can observe a inflation of the surface as an effect of the electric field. The study of electron doped compound Ga0,91Zn0,15Ta4Se8 show that if doping induce a metallicity, the transition induced by the electric pulse is closer to a bandwith controled transition rather than a doping controled transition. This manuscript set the question if this phenomena isintrinsic to GaTa4Se8, or general to the other weak Mott insulators
El, Ourzaz Lahcen. "Mesures diélectriques et caractérisation de matériaux moléculaires". Lyon 1, 1989. http://www.theses.fr/1989LYO10064.
Texto completoLouis, Christel. "Mélanges de polysulfones avec un élastomère acrylate : caractérisation morphologique et thermo-mécanique". Toulon, 2001. http://www.theses.fr/2001TOUL0002.
Texto completoBabicz, Sylvain. "Etude diélectrique des isolants plats anodisés pour la conception de machines électriques". Thesis, Artois, 2016. http://www.theses.fr/2016ARTO0204/document.
Texto completoThe use of state of the art organic enamels, capable to withstand 280 °C, makes the temperature class increase of electrical machine reaching its maximum. A technological breakthrough can be found by the substitution of organic enamel by a ceramic based insulation. Those materials are good dielectrics and their temperature resistance is very high compared to a classical technology. In this work, the studied conductor is an aluminum tape which insulation is obtained by an anodisation, an electrochemical process. This surface treatment makes the aluminum oxidizing: a thin layer of a few micrometres is obtained, thus representing the insulation layer of the conductor. The objectives of those PhD works is to identify and characterize this particular type of conductor so as to demonstrate the ability of using an anodized aluminum tape to makeelectrical machine running up to 400 °C. Measurements of PDIV, PDEV, and breakdown voltage are carried under various environmental conditions (temperatures varying from -70 °C up to 650 °C, variable humidity level). The use of an inverter to supply this high temperature machine induces steep fronts and over voltages. As a consequence, a theoretical model of a coil, made with this kind of conductor, is then proposed and based upon the impedance spectrum of the coil. The aim of this model is to help the designer to predict the first over voltage amplitude and to make the insulation of the first coil according to that. At least, a coil insulation improvement is depicted, using boron oxide: an impregnation is held to reinforce the alumina layer on the edge of the tape
Paillet, Philippe. "Effet du procédé de fabrication des isolants sur la charge d'espace créée par rayonnements X : application aux technologies silicium sur isolant". Montpellier 2, 1995. http://www.theses.fr/1995MON20042.
Texto completoMary-Tomic, Dominique. "Mise en évidence et étude de la luminescence des polymères isolants sous champ électrique ou en interaction avec un plasma froid : application au diagnostic". Toulouse 3, 1994. http://www.theses.fr/1994TOU30241.
Texto completoSalles, Laurent. "Effets du bombardement ionique sur les propriétés électriques du polycarbonate et du PMMA : mesure de la résistivité superficielle, des charges d'espace et analyse de la graphitisation induite". Caen, 2013. http://www.theses.fr/2013CAEN2001.
Texto completoPolymers are well appreciated materials in the field of electric and electronic components manufacturing, due to their excellent volume insulating properties. However, they have poor surface antistatic properties. Processes like ion bombardment can solve this problem. Polycarbonate and polymethylmethacrylate have been implanted by ions of various weights at different fluences, extraction tensions and ion flows. Surface resistivity has been measured and it has been demonstrated that this treatment makes these values decrease up to 8 orders of magnitude, without changing the volume resistivity. The influence of each parameter has been studied: all of them make the resistivity decrease when they increase. Space charges trapped into the matter have been studied by the means of the Alternating Thermal Waves Method. The samples that have been treated on the strongest conditions are the ones with the lowest space charges density. Formation of graphite nano-clusters is reported in scientific publications to be the cause of the change in electrical properties. Raman spectrometry analyses have been performed to detect this change in chemical structure. Some of the less resistive samples exhibit the signs of this kind of carbon whereas others do not, probably because of their lower implantation depth. The analysis of one very resistive sample has surprisingly revealed that he also contains graphite nano-clusters
Vallayer, Bruno. "Développement d'une méthode de caractérisation des matériaux isolants : la méthode du miroir : Application à l'étude des propriétés de charge d'oxydes". Ecully, Ecole centrale de Lyon, 1995. http://www.theses.fr/1995ECDL0014.
Texto completoWhen a negative electrical charge is trapped in an insulating material, this charge change the opertion of a secondary emission microscope and an image of the chamber appears on the screen. This physical phenomena call "the mirror effect" is well known and we have used it in order to measure the net negative charge trapped in the observed sample, after irridiation of this sample by a high energy electron beam. It has been necessary to develop a theoritical model of the problem, based on electrical field numerical calculation by a finite element code and on analytical optical calculation of the electron trajectories as a function of the system parameters. Then, we have used this nex method, called "the mirror method", in order to determine the charging properties of different ceramics : the tests performed on some "perfect" single-crystal ceramics (MgO, Sapphire, Rubis, SiO2, Y2O3), after recrystalisation, allow to propose a trapping model wich explain the experimental results. The tests performed on the same single-crystals before the recrystalisation, have shown the influence of the machining of those materials on their trapping properties. Finally, some technological polycrystalline ceramics have been tested in order to link their trapping properties to their electrical breakdown behaviour. It has been possible to understand the different problems raised by these experimental results, thanks to some Space Charge Physics basis concepts. Associating this physical theory with an experimental method as the Mirro Method appears to be very interesting for the study of the behaviour of the dielectrical materials
Chauvet, Christian. "Mise au point d'une méthodologie pour des essais de rupture a court terme en vue de la caractérisation des isolants synthétiques des cables haute-tension". Toulouse 3, 1992. http://www.theses.fr/1992TOU30073.
Texto completoLimelette, Patrice. "Propriétés de transport de systèmes électroniques fortement corrélés". Phd thesis, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00003545.
Texto completoReyes-Melo, Martin Edgar. "Modélisation des manifestations mécanique et diélectrique de la viscoélasticité des isolants organiques par la méthode de dérivation et d'intégration fractionnaire". Toulouse 3, 2004. http://www.theses.fr/2004TOU30086.
Texto completoKhazaka, Rabih. "Étude du vieillissement de polymères isolants utilisés dans le packaging des modules de puissance haute température". Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1454/.
Texto completoThe trend for integration and/or high ambient temperature operation of power electronics modules induces higher electrical and thermal stresses on their components. Based on a bibliographic study that allows evaluating different structures of packaging able to operate at high temperatures, thin dielectric layers are needed in order to insulate the different parts of the module. Therefore, the aim of this work was to define the potentiality of two dielectric polymers to operate at high temperatures (the first one is a polyimide BPDA-PDA and the second one is a fluorinated parylene PA-HT), and to be used as passivation layer for silicon carbide semiconductors or as dielectric layer between and on the metal frames. In order to reach the objective, characterizations of the dielectric properties up to 400 °C at the initial time (noted as t0) were performed. Then, the properties evolution (especially electrical ones) during the thermo-oxidative aging for temperature higher than 250 °C and long periods (several thousands of hours) were controlled periodically. At t0, the films show a good dielectric strength and the breakdown field remain higher than 2 MV/cm for the thicker tested films (8 µm). The DC conductivity show semi-resistive values for the BPDA-PDA between 300 °C and 400 °C and the values vary between resistive and semi-resistive ones for the PA-HT in the same temperature range. During the aging under N2, no degradation is observed up to 360 °C for BPDA-PDA polyimide. At 300 °C in air, stability of the breakdown voltage is observed when the BPDA-PDA is aged on Si substrate, while a slow degradation depending on the initial thicknesses is observed for films deposited on stainless steel substrate (S. S. ). This degradation, related to the oxygen presence in air, affect the surface layer and is thermally activated. The degradation appears also for BPDA-PDA on Si substrate at 360 °C in air. The PA-HT films were deposited on S. S. Substrates and aged in air at 300 °C, 340 °C and 360 °C. Results show the potentiality of the material for 300 °C application, with the occurring of cold crystallization that improves the low field dielectric properties. For the higher tested temperatures, thin films (5 µm) seem to be unsuitable for long periods applications and cannot pass 1000 hours at 360 °C. Hence, based on the initial dielectric properties and their evolution during the aging, the two polymers seems to be suitable for 300 °C applications. However, for higher temperatures (360 °C), the stability in air of the two materials, especially on the S. S. Substrate is not insured. Otherwise, solutions against the thermo-oxydative aging seem promising, and thermal treatments allowing the improvement of the electrical resistivity at the initial time are proposed
Ambid, Matthieu. "Evaluation de nanocomposites polypropylène/silicate pour l'isolation électrique : étude des phénomènes de polarisation, de conduction et des propriétés optiques". Toulouse 3, 2007. http://thesesups.ups-tlse.fr/795/.
Texto completoThis thesis focuses on polyolefin matrix nanocomposite. The goal is to provide an interpretation on their macroscopic properties. We studied electrical properties, optical and chemicophysical properties of composite materials based on iso- and syndiotactic polypropylene matrix and dispersions belong to the generic class of silicates. The means employed on measures dynamic dielectric analysis, current in the time domain, electroluminescence, photoluminescence and UV-visible spectroscopy. A method of time-frequency inversion was implemented : it allows to explain the transient currents observed from the frequency data and identify the regimes of field where nonlinear phenomena occur
Henri, Victor. "Identification et analyse des marqueurs de vieillissement pour polymères isolants sous contrainte thermique en aéronautique". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30066.
Texto completoThis work deals with the determination of ageing markers of high-performance polymers for electrical insulation applications in aeronautics. Most of power cables are made of a successive winding of poly(tetrafluoroethylene) PTFE and poly(imide) PI. This research is focused on the effects of thermal ageing on the physico-chemical structure of these polymers in order to link them to changes in thermomechanical and electrical behaviours. For PTFE, enthalpic and mechanical relaxations are strongly impacted by changes in chemical structure associated to a depolymerisation mechanism. The values of the enthalpy of crystallization and of the amplitude of the ß mechanical relaxation associated with the crystal/crystal transition, can be used as markers of thermal ageing for PTFE. For PI, changes in the chemical structure associated to the scission - recombination mechanism, highlight the formation of heterogeneities, modifying sorption process and electrical charge transport as measured in broadband dielectric spectroscopy. The evolution of the diffusion mechanism and of the activation energy of the electrical conductivity, constitute pertinent ageing markers for PI
Dubost, Vincent. "Étude par microscopie/spectroscopie tunnel de la transition isolant/métal induite par pulses électriques dans GaTa4Se8". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00496843.
Texto completoHuang, Xiao Lin. "Étude de l'évolution de la morphologie et des propriétés électriques du polytétrafluoroéthylène (PTFE) pour des applications aéronautiques en hautes températures (250 - 400 °C)". Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2490/.
Texto completoThe use of organic electrical insulators for electric cables has many advantages, such as their flexibility, lightness, good dielectric properties, etc. They are widely used in aeronautic domain. In a real operating environment of organic insulators, many factors may decrease their isolation performance over time: oxygen, moisture and salt spray in atmosphere, high temperature, application of operating voltage, machine vibration, radiation phenomena, etc. With technology development and new design of machines more efficient, insulators may undergo more severe stresses, therefore aging and degradation studies of dielectric materials in this context become more and more important. The organic insulators that we have investigated are used in electric insulators for ignition cables of helicopters. This kind of cable is located in hot area near engine, where electric insulators work in a severe environment (high temperature, high electric field, presence of moisture and oxygen, etc. ). For new generations of engine, the maximum operating temperature is much higher (approximately 350 °C), which may cause acceleration of end-of-life of insulator. Our research work particularly focuses on effect of thermal stress on aging and/or degradation of actually used organic insulators. The objective of our research work is study of usage limit, aging and degradation mechanisms of electric insulator, which is performed by physical-chemical, thermal and electrical characterization methods. The end portion of the cable is connected to the plug connector, cable insulator (PTFE) may undergo maximum operating temperature of about 340 °C, which is higher that the melting temperature (327 °C). Therefore we quantified the behaviour of PTFE at temperature higher than the melting point. We have two kinds of sample for characterization: thin films and cables. In order to study aging and degradation process of insulators (PTFE and PI) under conditions close to reality, samples were aged in air at constant temperatures ranging from 250 to 400 °C for durations ranging from several hours to several hundred hours. We have studies thermal stability, degradation kinetics, chemical structure and molecular morphology evolution of insulators by using several technics: TGA, FTIR, DSC. Chemical structure, molecular and surface morphology, dielectric strength evolution as well as partial discharges phenomena between metal sheath and cable insulator were also characterized
Lahoud, Nadine. "Modélisation du vieillissement des isolants organiques sous contrainte électrique : application à la fiabilité des matériaux". Toulouse 3, 2009. http://thesesups.ups-tlse.fr/517/.
Texto completoThe aim of this study is to improve the description of solid organic insulators or polymers ageing under electrical stress. With this objective in view, the different ageing scenarios existing in the literature were analyzed, compared and improved. This theoretical study showed that many parameters related to their heterogeneous structure and the distribution of their properties were neglected in order to simplify the modelling. This study presents a new approach in the description of solid organic insulators ageing by taking into consideration their experimentally demonstrated structural complexity. In this approach, the polymer material has been assimilated to a set of sites representing different energy states, thereby different properties as well as ageing rates depending on each site. The principal parameters involved during the ageing process, such as the specific volume variation, the dielectric strength evolution and the local value of the electrical field have been defined. The expression of the retardation time specific to each elementary ageing process has been established. Finally, a distributed form of those retardation times has been presented. Our "phenomenological" approach is thus a multi-sites one permitting, along with an experimental study, to establish an equation relating the life time of polymer electrical insulators to the different parameters at play, all along respecting their distribution over the entire set of sites within the polymer
Cherifi, Abderrezak. "Contribution à l'étude des charges d'espace dans les polymères isolants utilisés en H. T. Améliorations de la méthode de l'onde thermique". Montpellier 2, 1993. http://www.theses.fr/1993MON20020.
Texto completoSantana, José. "Mesure de charges d'espace dans les câbles de transport de l'énergie électrique". Montpellier 2, 1994. http://www.theses.fr/1994MON20030.
Texto completoSaifi, Ali. "Contribution à l'étude des propriétés magnétiques des systèmes spinelles isolants CdCr2xIn2-2xS4 et ZnCr2xGa2-2xO4 : phases type verre de spin". Paris 6, 1986. http://www.theses.fr/1986PA066519.
Texto completoEscaich, David. "Caractérisation et élaboration de couches de carbones amorphes hydrogènes à propriétés optiques par procédés plasmas". Toulouse 3, 2006. http://www.theses.fr/2006TOU30074.
Texto completoBrière, Benjamin. "Propriétés optiques de matériaux à fortes corrélations électroniques en conditions extrêmes". Thesis, Tours, 2018. http://www.theses.fr/2018TOUR4020/document.
Texto completoMaterials with strongly correlated electrons belong to the most intriguing systems in condensed matter physics due to their great variety of properties discovered during the last decades such as high temperature superconductivity, molecular conductors and colossal magnetoresistance. During this thesis, two types of strongly correlated materials have been studied: the quadruple perovskite EuCu3fe4Oi2 and the molecular conductors [Au(Et-thiazdt)2J. EuCu3Fe4Oi2 undergoes a metal to insulator transition at low temperature (240K), and [Au(Et-thiazdt)2J goes from a Mott insulator to a correlated metal state under high pressure. Infrared microspectroscopy measurements allowed us to probe the low energy electrodynamic of these systems. Ab-initio calculations were also used to understand the mechanisms of the transitions and the role of electronic correlations in the material
Guffond, Raphaël. "Characterization and modeling of microstructure evolution of cable insulation system under high continuous electric field". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS039/document.
Texto completoThis thesis presents a research work on understanding and modeling the electrical behavior of insulation system in cables subjected to high DC constraints. Electrical properties of polymeric insulation are directly related to their chemical and physical heterogeneities present at several scales. In this work, a new model is developed to simulate the modification over time of the microstructure in insulation polymers under electric field and temperature as well as the subsequent impacts on electrical properties. In this model, matrices are used to describe the distribution of each heterogeneity and electrical property in semi-crystalline polymer. When stressed under electric field and at temperature, matrices of microstructure evolve from implemented genetic laws. This simulated microstructure evolution yields to the simulation of electrical property changes over time at transient and steady state. To define these genetic laws, a detailed characterization of the physical, chemical and electrical properties of specific materials as a function of temperature and electric field is experimentally performed. Genetic laws are notably implemented to take into account the impact of the semi-crystalline structure and the presence of chemical residues in polymer electrical properties. Based on these genetic evolution laws, this modeling approach allows simulating DC electrical behavior of polymers only from their physical and chemical characterizations and reproduce accurately experimental electrical behavior with a faster solving time compared to other simulation methods
Lagoute, Jérôme. "Images et fluctuations du courant sur surfaces métalliques et fils moléculaires adsorbés en microscopie à effet tunnel". Toulouse 3, 2003. http://www.theses.fr/2003TOU30068.
Texto completoDougassa, Yvon. "Propriétés de transport et solubilité des gaz dans les électrolytes pour les batteries lithium-ion". Thesis, Tours, 2014. http://www.theses.fr/2014TOUR4035/document.
Texto completoThe performance and the safety of a lithium-ion battery depend to a great extent on the stability of the electrolyte solution, because the high voltage of the battery may cause the decomposition of lithium salt or organic solvents, which limits then the battery lifetime. During these degradations, several gases are, generally, generated like the CO2, CO, CH4 and C2H4, which induce in fact several problems related to the pressure increase inside the sealed cell. The main objective of this PhD thesis is to understand the key thermodynamic parameters which drive the gas dissolution in classical solvents and electrolytes. For that, several pure solvents and electrolytes have been firstly investigated to determine their volumetric and transport properties, as well as, their vapour pressure as the function of temperature and composition
Houssat, Mohammed. "Nanocomposite electrical insulation : multiscale characterization and local phenomena comprehension". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30211.
Texto completoIn the electrical insulation field, it was demonstrated that nanocomposite (NC) organic/inorganic hybrid materials assure a distinct improvement of their high temperature/high voltage functioning and allow the electrical insulation to strengthen its dielectric properties. Recently, it was shown that some modifications of the electrical properties such as permittivity, dielectric breakdown, partial discharges resistance or lifetime are often awarded to the nanoparticle/matrix interphase, a region where the presence of the nanoparticle changes the matrix properties. Moreover, recent studies show that the nanoparticle surface functionalization allows a better dispersion of the particles within the host matrix. This better dispersion affects the interphase zone and plays a major role in the nanocomposite properties improvement as well. However, the role of the interphase remains theoretical and few experimental results exist to describe this phenomenon. Accordingly, because of its nanometer scale, the interphase properties characterization remains a challenge. Two main studies are carried out, during this thesis work, that can provide a better understanding of structure-properties relationships in polymer nanocomposite. First, Atomic Force Microscopy (AFM) is employed to make at the same time qualitative and quantitative measurements of these interaction zones within Polyimide/Silicon Nitride (PI/Si3N4) nanocomposite. The Peak Force Quantitative Nano Mechanical (PF QNM) AFM mode reveals the presence of the interphase by measuring mechanical properties (Young modulus, deformation or adhesion). Electrostatic force microscope (EFM) mode is used in order to detect and measure the matrix and interphase local permittivity. Moreover, the aim of this work is to present the effect of the surface functionalization of silicon nitride (Si3N4) nanoparticles on the interphase regions. Mechanical and electrical quantitative results permit comparing the interphase dimension and properties between treated and untreated Si3N4 nanoparticles. As a result, this new approach to characterize the nanocomposite interphase zone using local measurements confronts experimental results with theoretical models. A new model based on the obtained experimental results is proposed. In addition, the second part of this study presents a macroscopic investigation on the dielectric properties and breakdown strength of neat polyimide, untreated and treated nanocomposite films. Results reveal the interphase role on the reduction of the electrode polarization (EP) phenomenon due to ionic movements especially at high temperatures. For untreated nanoparticles, these effects are less important due to the aggregate formation. In contrast, an EP drastic decrease is obtained by functionalizing the nanofiller surface with a silane coupling agent. Finally, the high temperature breakdown strength for all samples is investigated and shows a considerable increase of nanocomposites dielectric performance at high temperature compared to neat PI
Ridene, Mohamed. "Propriétés Structurales et Électroniques du Graphène Épitaxié sur Carbure de Silicium". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112232.
Texto completoThe synthesis of graphene by thermal decomposition of silicon carbide (SiC) is a promising technique for the integration of this new material in the industry, especially in electronic devices. The advantage of this method lies in the growth of macroscopic graphene films directly on an insulator substrate. However, before using this material in electronic devices, it is advisable to control its synthesis and modulate its properties. In this thesis, we present the structural and electronic properties of graphene obtained by graphitization of 3C- , 4H - and 6H- SiC polytypes. Various characterization methods were used, including low energy electron diffraction (LEED) and microscopy and scanning tunneling spectroscopy (STM / STS). Based on STM / STS measurements, we show that the discontinuity of epitaxial graphene at the step edges may introduce an additional lateral confinement of electrons in graphene. The observation of Van Hove singularities in the STS spectra confirmed the one dimensional confinement of graphene in step bunching regions of SiC.Finally, we show that when disorder is introduced on our graphene samples, the charge carrier density is reduced. This disorder lead to the observation of a quantum phase transition from a localized regime to a quantum Hall effect regime
Baudon, Sylvain. "Etude de l'influence des contraintes appliquées sur l'évolution des propriétés diélectriques des couches minces isolantes dans les composants semi-conducteurs de puissance". Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2013. http://tel.archives-ouvertes.fr/tel-01001950.
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