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I N Mihailescu - One of the best experts on this subject based on the ideXlab platform.

  • Chromium Oxides mixtures in pld films investigated by raman spectroscopy
    Journal of Optoelectronics and Advanced Materials, 2010
    Co-Authors: O Monnereau, Laurence Tortet, C E A Grigorescu, D Savastru, C R Iordanescu, F Guinneton, R Notonier, A Tonetto, T Zhang, I N Mihailescu
    Abstract:

    The composition of Pulsed Laser Deposited thin films from Cr8O21 targets has been investigated by Raman spectroscopy. To this purpose we have prepared the Chromium Oxides Cr8O21, Cr2O5, CrO2 and Cr2O3 in bulk form to provide standard Raman spectra for characterisation of the samples. The range of Oxides has been prepared by thermal decomposition of CrO3 following the thermo-gravimetric analysis. CrO2 was obtained by two other specific ways, i.e. hot pressing of Cr8O21 and hydrothermal synthesis. Structural characterization was performed by X-ray diffraction, SEM, IR and Raman spectroscopy. Raman investigation is demonstrated to have the capacity to identify CrO2 as well as trace concentrations of secondary phases in the PLD thin films. The Raman measurements have led us also to the conclusion that PLD of Cr8O21 targets yields in thin films containing either mixtures of (Cr2O5, CrO2 and Cr2O3) or, under particular conditions of oxygen pressure and substrate temperature, of (CrO2 and Cr2O3) only.

  • Chromium Oxides thin films prepared and coated in situ with gold by pulsed laser deposition
    Materials Science and Engineering B-advanced Functional Solid-state Materials, 2005
    Co-Authors: D Stanoi, O Monnereau, Laurence Tortet, F Guinneton, T Zhang, G Socol, C Grigorescu, I N Mihailescu
    Abstract:

    Abstract Chromium dioxide is a very suitable compound for spintronic devices. It is ferromagnetic at room temperature ( T c  = 395 K) and has a half-metallic band structure. CrO 2 has been theoretically predicted to be100% spin polarized at the Fermi level. For some applications in spintronics low deposition temperatures are required. However, the fabrication of single phase thin films of CrO 2 at low temperature is quite difficult due to its metastable character. In this work we report our experiments to deposit thin films of Chromium Oxides by reactive pulsed laser deposition (RPLD). RPLD experiments were performed with a UV KrF* excimer laser source ( τ FWHM  ≥ 20 ns, λ  = 248 nm) in different conditions regarding the target, the substrate temperature, the atmosphere inside the deposition chamber and the laser fluence. In order to prevent the reduction of CrO 2 to Cr 2 O 3 in thin films preserved in ambient conditions some of the samples were capped with gold in situ using the same set-up. The composition and morphology of the deposited films were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. A higher and stable content of CrO 2 in the deposited films was evidenced in the case of samples capped with Au. Subsequent analysis performed after 4 months showed no difference in the content of the film.

Jong Shik Chung - One of the best experts on this subject based on the ideXlab platform.

  • Catalytic fluorination of 1,1,1‐trifluoro‐2‐chloroethane (HCFC‐133a) over Chromium catalysts
    Catalysis Letters, 1998
    Co-Authors: Jong Shik Chung
    Abstract:

    Catalytic fluorination of HCFC‐133a was performed over various forms unsupported and supported Chromium Oxides. Catalytic activity is strongly dependent on the morphological structure of chromia. Increased conversion is observed as the crystallinity of chromia decreases. The best catalytic activity and strongest resistance against deactivation observed with CrOx/MgO is attributed to the presence of highly dispersed Chromium species (isolated Cr(VI) and oligomeric Cr–O–Cr species) on the support surface.

Qin Zhong - One of the best experts on this subject based on the ideXlab platform.

  • insights into synergistic effect of Chromium Oxides and ceria supported on ti pilc for no oxidation and their surface species study
    Applied Surface Science, 2015
    Co-Authors: Lei Zhong, Wei Cai, Qin Zhong
    Abstract:

    Abstract The insights of synergistic effect between Chromium Oxides and ceria supported on Ti-PILC were studied for NO oxidation. The aim of this study was to investigate the role of Chromium Oxides and ceria and their synergistic effect in textural properties, redox performance and surface species over the Cr1−xCex/TP catalysts. These catalysts were investigated in detail by means of Brunauer–Emmertt–Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscope (TEM), temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption (NO-TPD, O2-TPD), photoluminescence spectra (PL), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It has been found that CrOx were beneficial to adsorb and activate NO to form NO+ and then generate nitrates while ceria were inclined to activate O2 via oxygen vacancies to produce nitrates. Besides, the results of in situ DRIFTS further demonstrated that surface species were associated with not only reaction atmosphere but also reaction temperature. Hence, a possible reaction model was tentatively proposed.

Christopher W Jones - One of the best experts on this subject based on the ideXlab platform.

Tsunehiro Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • photocatalytic oxidation of propylene with molecular oxygen over highly dispersed titanium vanadium and Chromium Oxides on silica
    Journal of Physical Chemistry B, 2006
    Co-Authors: Fumiaki Amano, Tsuyoshi Yamaguchi, Tsunehiro Tanaka
    Abstract:

    Photocatalytic oxidation of propylene with molecular oxygen at room temperature was investigated over various silica-supported metal Oxides with low loading. The photocatalytic active site is assumed to be the isolated tetrahedrally coordinated metal Oxides in the ligand-to-metal charge-transferred state, such as (M δ- -O L δ+ )*. Photocatalytic epoxidation of propylene into propylene oxide was promoted over silica-supported V and Ti Oxides at steady state. Over silica-supported Cr oxide, the propylene oxide formation rate was remarkably decreased with the time course in the reaction. The oxidation state and the coordination environment of the supported Ti, V, and Cr oxide species were determined by diffuse reflectance UV-vis spectroscopy (DRS) and electron spin resonance (ESR). During the photocatalytic oxidation, the oxidation state of the Ti 4+ species was not varied. On the other hand, the V 5+ species was partially reduced to V 4+ and the Cr 6+ species was successively reduced to Cr 5+ and Cr 3+ . An isotopic tracer study of the C 3 H 6 - 18 O 2 reaction suggests the difference of the active oxygen species between TiO 2 /SiO 2 and V 2 O 5 /SiO 2 . The active oxygen species on TiO 2 /SiO 2 is derived from molecular oxygen. On the other hand, the photogenerated products on V 2 O 5 /SiO 2 incorporate the lattice oxygen of the surface metal oxide species. It is suggested that the kinds of terminal ligand (hydroxyl or oxo) of the tetrahedrally coordinated metal Oxides on silica decide the active oxygen species in the photocatalytic oxidation. A photoinduced hole center on the monohydroxyl (SiO) 3 Ti-OH species activates molecular oxygen that reacts with propylene. In the case of the monooxo (SiO) 3 V=O and dioxo (SiO) 2 Cr=O 2 species, the photoactivated lattice oxygen (O L - )* directly reacts with propylene.