Sol gel synthesis of multiphase lanthanum oxicarbonate and langasite thin films

Precursors of lanthanum oxide and of (3La2O3, 5Ga2O3, SiO2) system were first elaborated then thermally decomposed into polycrystalline lanthanum oxide and langasite La3Ga5SiO14. The as prepared lanthanum oxide powder was then hydrated and carbonated to give hydroxicarbonates: thermal decomposition of these complex system La2O3-X(OH)y(CO3)z was studied by Fourier Transform infrared spectroscopy. Spin coating process applied to these precursors was optimized to elaborate thin films of lanthanum oxicarbonate La2O2CO3, lanthanum oxide La2O3 and langasite, on silicium substrates (Si-(001)). Thin films are partly textured. Making use of same spin coating process, multiphase thin films of langasite covered with La2O3 particles were obtained.Precursors of lanthanum oxide and of (3La2O3, 5Ga2O3, SiO2) system were first elaborated then thermally decomposed into polycrystalline lanthanum oxide and langasite La3Ga5SiO14. The as prepared lanthanum oxide powder was then hydrated and carbonated to give hydroxicarbonates: thermal decomposition of these complex system La2O3-X(OH)y(CO3)z was studied by Fourier Transform infrared spectroscopy. Spin coating process applied to these precursors was optimized to elaborate thin films of lanthanum oxicarbonate La2O2CO3, lanthanum oxide La2O3 and langasite, on silicium substrates (Si-(001)). Thin films are partly textured. Making use of same spin coating process, multiphase thin films of langasite covered with La2O3 particles were obtained

Synthesis and characterization of nanosized Ce1−xbixo2−δ solid solutions for catalytic applications

AbstractThis study consists of elaborating and characterizing some nanometric materials in basic of rare-earth oxides by the soft chemistry technique. the first step of this work consists of synthesizing nanometric pure ceria by sol-gel process. In the second one, the Bismuth doped ceria by co-precipitation method was realized in order to obtain ceria-based solid solution, to improve its catalytic property by creation of oxygen vacancies. The solubility limit of Bi2O3 in CeO2 was determined to be around 20 atom %. The effect of thermal treatment temperatures on the average crystallite sizes and lattice parameters was done for pure ceria and Ce1−xBixO2−x/2 (x = 0.15 and 0.2). The different elaborated samples are subject of structural characterization (XRD). Catalytic reactivity of these materials in presence of “air- toxic gas” mixtures is studied by Fourier Transform Infra-Red Spectroscopy (FTIR)

Electrical conductivity of BaCeO3 synthesized by new sol-gel method

Polycrystalline BaCeO3 was prepared using new sol-gel processing at low temperature. The sample was characterized by X- ray diffraction and transmission electronic microscopy. The refined lattice parameters were found to be equal to: a = 8.782 Å, b = 6.240 Å, c = 6.217 Å. Electrical conduction was studied in the temperature range 150 to 950°C. The apparent conductivity of compacted samples was found to increase with temperature in a non linear way, from σ =2.49 10-7 S.m-1 at T =150°C to σ = 1.55 10-3S.m-1 at T =950°C. The activation energy is not constant and was found to increase from about 0.21 eV (in the temperature range: 150°C - 450°C) to 0.94 eV (in the temperature range 450°C - 950°C)Polycrystalline BaCeO3 was prepared using new sol-gel processing at low temperature. The sample was characterized by X- ray diffraction and transmission electronic microscopy. The refined lattice parameters were found to be equal to: a = 8.782 Å, b = 6.240 Å, c = 6.217 Å. Electrical conduction was studied in the temperature range 150 to 950°C. The apparent conductivity of compacted samples was found to increase with temperature in a non linear way, from σ =2.49 10-7 S.m-1 at T =150°C to σ = 1.55 10-3S.m-1 at T =950°C. The activation energy is not constant and was found to increase from about 0.21 eV (in the temperature range: 150°C - 450°C) to 0.94 eV (in the temperature range 450°C - 950°C)

Structural and Raman Vibrational Studies of CeO

A series of ceramics samples belonging to the CeO2-Bi2O3 phase system have been prepared via a coprecipitation route. The crystallized phases were obtained by heating the solid precursors at 600∘C for 6 hours, then quenching the samples. X-ray diffraction analyses show that for x<0.20 a solid solution Ce1−xBixO2−x/2 with fluorine structure is formed. For x ranging between 0.25 and 0.7, a tetragonal β′ phase coexisting with the FCC solid solution is observed. For x ranging between 0.8 and 0.9, a new tetragonal β phase appears. The β′ phase is postulated to be a superstructure of the β phase. Finally, close to x=1, the classical monoclinic α Bi2O3 structure is observed. Raman spectroscopy confirms the existence of the phase changes as x varies between 0 and 1

Hydrostatic compression on YBa2_{2}Cu3_{3}O7−δ_{7-\delta}/polymer composites

High-Tc superconducting YBa$_{2}$Cu$_{3}$O_{7\mbox{-}\delta} phase was produced by a solid state reaction method. A series of YBa$_{2}$Cu$_{3}$O_{7\mbox{-}\delta}/polymer composites were fabricated. The structure, physical property, levitation and mechanical strength of composites were carried out. The Meissner effects associated with the 91K superconducting transition were found to be roughly preserved in the composites. Elastic experiments are carried out by applying a uniaxial pressure. Young's modulus of compression and compressibility was calculated. It increases with the volume fraction $\Phi$ s of superconductor. Poisson's coefficient was determined. The role of contacts between component is discussed

Modélisation des propriétés électriques d'un composite supraconducteur

Le comportement électrique d'un composite à base de supraconducteur est simulé par un circuit comprenant divers éléments RLC montés en parallèle et/ou en série. Une justification en termes de constituants du composite est donnée à chaque composant élémentaire du modèle. L'impédance du circuit est calculée en fonction des trois variables : température, fréquence et fraction volumique du supraconducteur

High photocatalytic activity for the degradation of rhodamine B in water

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