Synthèse du LiXFePO4 par voie fondue et l’étude de la couche de carbone sur LiFePO4

Le LiFePO4 est un matériau prometteur pour les cathodes des batteries au lithium. Il possède une bonne stabilité à haute température et les précurseurs utilisés pour la synthèse sont peu couteux. Malheureusement, sa faible conductivité nuit aux performances électrochimiques. Le fait de diminuer la taille des particules ou d’enrober les particules d’une couche de carbone permet d’augmenter la conductivité. Nous avons utilisé une nouvelle méthode appelée « synthèse par voie fondue » pour synthétiser le LiFePO4. Cette synthèse donne des gros cristaux et aucune impureté n’est détectée par analyse Rayon-X. En revanche, la synthèse de LiXFePO4 donne un mélange de LiFePO4 pur et d’impureté à base de lithium ou de fer selon l’excès de fer ou de lithium utilisé. La taille des particules de LiFePO4 est réduite à l’aide d’un broyeur planétaire et plusieurs paramètres de broyage sont étudiés. Une couche de carbone est ensuite déposée sur la surface des particules broyées par un traitement thermique sur le LiFePO4 avec du -lactose. L’influence de plusieurs paramètres comme la température du traitement thermique ou la durée du chauffage sont étudiés. Ces expériences sont réalisées avec un appareil d’analyse thermogravimétrique (ATG) qui donne la quantité de chaleur ainsi que la variation de masse durant le chauffage de l’échantillon. Ce nouveau chauffage pour la couche de carbone donne des échantillons dont les performances électrochimiques sont similaires à celles obtenues précédemment avec la méthode de chauffage pour la couche de carbone utilisant le four tubulaire.

Écriture, altérité et identité dans La quarantaine de JMG Le Clézio

L’œuvre de JMG Le Clézio se caractérise par sa perpétuelle évolution. Elle échappe aux classifications génériques et maintient son statut subversif et indépendant. L’écriture de cet écrivain traduit les diverses influences qui l’ont marqué, les problèmes auxquels il fait face et la thématique majeure dans laquelle il inscrit son œuvre. À travers l’étude de La quarantaine, paru en 1995, nous essayerons lors du premier chapitre de comprendre comment Le Clézio réinvente son écriture pour remédier au problème de l’impureté du langage qui caractérisait son œuvre d’avant les années quatre-vingts. Dans le deuxième chapitre, nous analyserons les thématiques littéraire, familiale et historique qui font de cet ouvrage un roman de filiation. La quarantaine insiste sur l’importance de l’altérité traditionnelle et non occidentale en tant que facteur dans ce changement romanesque, et dont le mode de vie réfléchit différemment le problème de l’identité chez l’individu occidental. Dans le troisième chapitre, nous aborderons la question des enjeux de l’identité à travers l’expérience initiatique à laquelle se livre le protagoniste de La quarantaine en quête d’un devenir identitaire, d’une émancipation qui réconcilie l’individu moderne avec soi-même.

Défauts et diffusion dans le silicium amorphe

Nous avons observé une augmentation ‘’transient’’du taux de cristallisation interfacique de l’a-Si lorsqu’on réimplante du Si à proximité de l’interface amorphe/cristal. Après amorphisation et traitement thermique à 650°C pendant 5s de la couche a-Si crée par implantation ionique, une partie a été réimplantée. Les défauts produits par auto-réimplantation à 0.7MeV se trouvent à (302±9) nm de l’interface initiale. Cela nous a permis d’étudier d’avantage la variation initiale de la vitesse SPE (Épitaxie en phase solide). Avec des recuit identiques de 4h à 500°C, nous avons déterminé les positions successives des interfaces et en déduit les taux de cristallisation SPE. La cristallisation débute à l’interface et continue graduellement vers la surface. Après le premier recuit, (252±11) nm s’est recristallisé dans la zone réimplantée soit un avancement SPE de 1.26x10^18at./cm2. Cette valeur est environ 1.50 fois plus importante que celle dans l’état relaxé. Nous suggérons que la présence de défauts à proximité de l’interface a stimulé la vitesse initiale. Avec le nombre de recuit, l’écart entre les vitesses diminue, les deux régions se cristallisent presque à la même vitesse. Les mesures Raman prises avant le SPE et après chaque recuit ont permis de quantifier l’état de relaxation de l’a-Si et le transfert de l’état dé-relaxé à relaxé.

Stability studies of intravenous cyclosporine preparations stored in non-PVC containers

Dans cette étude, la stabilité de préparations intraveineuses de cyclosporine (0.2 et 2.5 mg/mL dans NaCl 0.9% ou dextrose 5%) entreposées dans des seringues de polypropylène, des sacs de polypropylène-polyoléfine et des sacs de vinyle acétate d’éthylène a été évaluée. Une méthode HPLC indicatrice de la stabilité à base de méthanol a été développée et validée suite a des études de dégradation forcée. Les solutions évaluées ont été préparées de façon aseptique, puis entreposées à 25°C. La stabilité chimique a été évaluée par HPLC et la stabilité physique a été évaluée par inspection visuelle et aussi par diffusion dynamique de la lumière (DLS). Tous les échantillons sont demeurés stables chimiquement et physiquement dans des sacs de polypropylène-polyoléfine (>98% de cyclosporine récupérée après 14 jours). Lorsqu’entreposés dans des seringues de polypropylène, des contaminants ont été extraits des composantes de la seringue. Toutefois, aucune contamination n’a été observée après 10 min de contact entre la préparation de cyclosporine non-diluée et ces mêmes seringues. Les préparations de 2.5 mg/mL entreposées dans des sacs de vinyle acétate d’éthylène sont demeurés stables chimiquement et physiquement (>98% de cyclosporine récupérée après 14 jours). Toutefois, une adsorption significative a été observée avec les échantillons 0.2 mg/mL entreposés dans des sacs de vinyle acétate d’éthylène (<90% de cyclosporine récupéré après 14 jours). Une étude cinétique a démontré une bonne corrélation linéaire entre la quantité adsorbée et la racine carrée du temps de contact (r2 > 0.97). Un nouveou modèle de diffusion a été établi. En conclusion, les sacs de polypropylène-polyoléfine sont le meilleur choix; les seringues de polypropylène présentent un risque de contamination, mais sont acceptables pour un transfert rapide. Les sacs de vinyle acétate d’éthylène ne peuvent être recommandés à cause d’un problème d’adsorption.

Growth and Characterization of ZnO based Heterojunction diodes and ZnO Nanostructuresby Pulsed Laser Ablation

Transparent conducting oxides (TCO’s) have been known and used for technologically important applications for more than 50 years. The oxide materials such as In2O3, SnO2 and impurity doped SnO2: Sb, SnO2: F and In2O3: Sn (indium tin oxide) were primarily used as TCO’s. Indium based oxides had been widely used as TCO’s for the past few decades. But the current increase in the cost of indium and scarcity of this material created the difficulty in obtaining low cost TCO’s. Hence the search for alternative TCO material has been a topic of active research for the last few decades. This resulted in the development of various binary and ternary compounds. But the advantages of using binary oxides are the easiness to control the composition and deposition parameters. ZnO has been identified as the one of the promising candidate for transparent electronic applications owing to its exciting optoelectronic properties. Some optoelectronics applications of ZnO overlap with that of GaN, another wide band gap semiconductor which is widely used for the production of green, blue-violet and white light emitting devices. However ZnO has some advantages over GaN among which are the availability of fairly high quality ZnO bulk single crystals and large excitonic binding energy. ZnO also has much simpler crystal-growth technology, resulting in a potentially lower cost for ZnO based devices. Most of the TCO’s are n-type semiconductors and are utilized as transparent electrodes in variety of commercial applications such as photovoltaics, electrochromic windows, flat panel displays. TCO’s provide a great potential for realizing diverse range of active functions, novel functions can be integrated into the materials according to the requirement. However the application of TCO’s has been restricted to transparent electrodes, ii notwithstanding the fact that TCO’s are n-type semiconductors. The basic reason is the lack of p-type TCO, many of the active functions in semiconductor originate from the nature of pn-junction. In 1997, H. Kawazoe et al reported the CuAlO2 as the first p-type TCO along with the chemical design concept for the exploration of other p-type TCO’s. This has led to the fabrication of all transparent diode and transistors. Fabrication of nanostructures of TCO has been a focus of an ever-increasing number of researchers world wide, mainly due to their unique optical and electronic properties which makes them ideal for a wide spectrum of applications ranging from flexible displays, quantum well lasers to in vivo biological imaging and therapeutic agents. ZnO is a highly multifunctional material system with highly promising application potential for UV light emitting diodes, diode lasers, sensors, etc. ZnO nanocrystals and nanorods doped with transition metal impurities have also attracted great interest, recently, for their spin-electronic applications This thesis summarizes the results on the growth and characterization of ZnO based diodes and nanostructures by pulsed laser ablation. Various ZnO based heterojunction diodes have been fabricated using pulsed laser deposition (PLD) and their electrical characteristics were interpreted using existing models. Pulsed laser ablation has been employed to fabricate ZnO quantum dots, ZnO nanorods and ZnMgO/ZnO multiple quantum well structures with the aim of studying the luminescent properties.

Investigations on Photoconductivity and Electrical Switiching in Selected Chalcogenide Glasses

In this thesis, we present the results of our investigations on the photoconducting and electrical switching properties of selected chalcogenide glass systems. We have used XRD and X-ray photoelectron spectroscopy (XPS) analysis for confinuing the amorphous nature of these materials and for confirming their constituents respectively.Photoconductivity is the enhancement in electrical conductivity of materials brought about by the motion of charge carriers excited by absorbed radiation. The phenomenon involves absorption, photogeneration, recombination and transport processes and it gives good insight into the density of states in the energy gap of solids due to the presence of impurities and lattice defects. Photoconductivity measurements lead to the determination of such important parameters as quantum efficiency, photosensiti\'ity, spectral sensitivity and carrier lifetime. Extensive research work on photoconducting properties of amorphous semiconductors has resulted in the development of a variety of very sensitive photodetectors. Photoconductors are finding newer and newer uses eyery day. CdS, CdSe. Sb2S3, Se, ZnO etc, are typical photoconducting materials which are used in devices like vidicons, light amplifiers, xerography equipment etc.Electrical switching is another interesting and important property possessed by several Te based chalcogenides. Switching is the rapid and reversible transition between a highly resistive OFF state, driven by an external electric field and characterized by a threshold voltage, and a low resistivity ON state, Switching can be either threshold type or memory type. The phenomenon of switching could find applications in areas like infonnation storage, electrical power control etc. Investigations on electrical switching in chalcogenide glasses help in understanding the mechanism of switching which is necessary to select and modify materials for specific switching applications.Analysis of XRD pattern gives no further infonuation about amorphous materials than revealing their disordered structure whereas x-ray photoelectron spectroscopy,XPS) provides information about the different constituents present in the material. Also it gives binding energies (b.e.) of an element in different compounds and hence b.e. shift from the elemental form.Our investigations have been concentrated on the bulk glasses, Ge-In-Se, Ge-Bi-Se and As-Sb-Se for photoconductivity measurements and In-Te for electrical switching. The photoconducting properties of Ge-Sb-Se thin films prepared by sputtering technique have also been studied. The bulk glasses for the present investigations are prepared by the melt quenching technique and are annealed for half an hour at temperatures just below their respective glass transition temperatures. The dependence of photoconducting propenies on composition and temperature are investigated in each system. The electrical switching characteristics of In-Te system are also studied with different compositions and by varying the temperature.

Size dependent fluorescence spectroscopy of nanocolloids of ZnO

In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.

Magnetic phase separation in ordered alloys

We present a lattice model to study the equilibrium phase diagram of ordered alloys with one magnetic component that exhibits a low temperature phase separation between paramagnetic and ferromagnetic phases. The model is constructed from the experimental facts observed in Cu3-xAlMnx and it includes coupling between configurational and magnetic degrees of freedom that are appropriate for reproducing the low temperature miscibility gap. The essential ingredient for the occurrence of such a coexistence region is the development of ferromagnetic order induced by the long-range atomic order of the magnetic component. A comparative study of both mean-field and Monte Carlo solutions is presented. Moreover, the model may enable the study of the structure of ferromagnetic domains embedded in the nonmagnetic matrix. This is relevant in relation to phenomena such as magnetoresistance and paramagnetism

Freezing of 4He and its liquid-solid interface from density functional theory

We show that, at high densities, fully variational solutions of solidlike types can be obtained from a density functional formalism originally designed for liquid 4He . Motivated by this finding, we propose an extension of the method that accurately describes the solid phase and the freezing transition of liquid 4He at zero temperature. The density profile of the interface between liquid and the (0001) surface of the 4He crystal is also investigated, and its surface energy evaluated. The interfacial tension is found to be in semiquantitative agreement with experiments and with other microscopic calculations. This opens the possibility to use unbiased density functional (DF) methods to study highly nonhomogeneous systems, like 4He interacting with strongly attractive impurities and/or substrates, or the nucleation of the solid phase in the metastable liquid.

Magnetic field effect on quantum corrections to the low-temperature conductivity in mettalic perovskite oxides

The transport and magnetotransport properties of the metallic and ferromagnetic SrRuO3 (SRO) and the metallic and paramagnetic LaNiO3 (LNO) epitaxial thin films have been investigated in fields up to 55 T at temperatures down to 1.8 K . At low temperatures both samples display a well-defined resistivity minimum. We argue that this behavior is due to the increasing relevance of quantum corrections to the conductivity (QCC) as temperature is lowered; this effect being particularly relevant in these oxides due to their short mean free path. However, it is not straightforward to discriminate between contributions of weak localization and renormalization of electron-electron interactions to the QCC through temperature dependence alone. We have taken advantage of the distinct effect of a magnetic field on both mechanisms to demonstrate that in ferromagnetic SRO the weak-localization contribution is suppressed by the large internal field leaving only renormalized electron-electron interactions, whereas in the nonmagnetic LNO thin films the weak-localization term is relevant.

Properties of Anisotropic Superconductors in SR Model

The present thesis deals with the theoretical investigations on the effect of anisotropy on various properties of magnetically doped superconductors described by fihiba — Rusinov model.Chapter 1 is introductory. It contains a brief account of the current status of theory of superconductivity. In’ chapter 2 we give the formulation of the problem. Chapter 2.1 gives the BCS theory. The effect of magnetic impurities in superconductors as described by A8 theory is given in chapter 2.2A and that described by SR model is discussed in chapter 2.28. Chapter 2.2c deals with Kondo effect. In chapter 2.3 the anisotropy problem is reviewed. Our calculations, results and discussions are given in chapter 3. Chapter 3.1 deals with Josephson tunnel effect. In chapter 3.2 the thermodynamic critical field H62 is described. Chtpter 3.3 deals with the density of states. The ultrasonic attenuation coefficient and ufitlear spin relaxation are given in chapter 3.4 and 3.5 respectively. In chapter 3.6 we give the upper critical field calculations and chapter 3.7 deals with the response function. The Kondo effect is given in chapter 3.8. In chapter 4 we give the sumary of our results

Growth And Characterization Of Te-Se System And Some Tei.I.Urioes

The physical properties of solid matter are basically influenced by the existence of lattice defects; as a result the study of crystal defects has assumed a central position in solid state physics and materials science. The study of dislocations ixa single crystals can yield a great deal of information on the mechanical properties of materials. In order to secure a full understanding of the processes taking place in semiconducting materials, it is important to investigate the microhardness of these materials-—the most reliable method of determining the fine structure of crystals, the revelation of micro—inhomogenities in the distribution of impurities, the effect of dislocation density on the mechanical properties of crystals etc. Basically electrical conductivity in single crystals is a defect controlled phenomenon and hence detailed investigation of the electrical properties of these materials is one of the best available methods for the study of defects in them. In the present thesis a series of detailed studies carried out in Te—Se system, Bi2Te3 and In2Te3 crystals using surface topographical, dislocation and microindentation analysis as well as electrical measurements are presented

Chemically Modified Glassy Carbon Electrode as Sensors for Various Pharmaceuticals

Voltammetric methods are applicable for the determination of a wide variety of both organic and inorganic species. Its features are compact equipment, simple sample preparation, short analysis time, high accuracy and sensitivity. Voltammetry is especially suitable for laboratories in which only a few parameters have to be monitored with a moderate sample throughput. Of various electrode materials, glassy carbon electrode is particularly useful because of its high electrical conductivity, impermeability to gases, high chemical resistance, reasonable mechanical and dimensional stability and widest potential range of all carbonaceous electrodes. Electrode modification is a vigorous research area by which the electrochemical determination of various analyte species is facilitated. The scope of pharmaceutical analysis includes the analytical investigation of pure drug, drug formulations, impurities and degradation products of drugs, biological samples containing the drugs and their metabolites with the aim of obtaining data that can contribute to the maximal efficacy and maximal safety of drug therapy. This thesis presents the modification of glassy carbon electrode using metalloporphyrin and dyes and subsequently using these modified electrodes for the determination of various pharmaceuticals. The thesis consists of 9 chapters.

Strain induced anomalous red shift in mesoscopic iron oxide prepared by a novel technique

Nano magnetic oxides are promising candidates for high density magnetic storage and other applications. Nonspherical mesoscopic iron oxide particles are also candidate materials for studying the shape, size and strain induced modifications of various physical properties viz. optical, magnetic and structural. Spherical and nonspherical iron oxides having an aspect ratio, ~2, are synthesized by employing starch and ethylene glycol and starch and water, respectively by a novel technique. Their optical, structural, thermal and magnetic properties are evaluated. A red shift of 0⋅24 eV is observed in the case of nonspherical particles when compared to spherical ones. The red shift is attributed to strain induced changes in internal pressure inside the elongated iron oxide particles. Pressure induced effects are due to the increased overlap of wave functions. Magnetic measurements reveal that particles are superparamagnetic. The marked increase in coercivity in the case of elongated particles is a clear evidence for shape induced anisotropy. The decreased specific saturation magnetization of the samples is explained on the basis of weight percentage of starch, a nonmagnetic component and is verified by TGA and FTIR studies. This technique can be modified for tailoring the aspect ratio and these particles are promising candidates for drug delivery and contrast enhancement agents in magnetic resonance imaging