Electrical properties and reactivity under air–CO flows of composite systems based on ceria coated carbon nanotubes

Nanocomposite systems of ceria nanoparticles and Double Walled Carbon Nanotubes (DWNTs) coated with nanoceria (nCeO2) were elaborated using a classical sol gel method. Three samples noted as [nCeO2 + xDWNTs] with variable weight fractions x = 0, 5 and 15 wt.% of DWNTs were obtained. The samples were characterized by Xray diffraction and electron microscopy. The electrical conductivity of [nCeO2 + xDWNTs] compacted pellets systems was determined from electrical impedance spectrometry, under air, between 120 and 400 °C. In this temperature range, all samples were semiconducting with a weak variation of activation energy. However, the conductivity strongly increased with the weight fraction of ceria coated carbon nanotubes. Finally, the solid–gas interactions between air–CO flows and these systems were studied as a function of time and temperature, by means of Fourier transform infrared (FTIR) spectroscopy. The oxidation kinetics of CO into CO2 was analyzed from the evolutions of FTIR absorption band intensities. As the carbon nanotube fraction x increased, the conversion efficiency was strongly improved

Distributed Photovoltaic Architecture for HVDC-bus Feeding with a Simple Evaluation of Optimal Tracking

International audienceThis contribution describes, compares, and analyses two structures and their operating modes dedicated to renewable energy production from photovoltaic (PV) sources. Between the two different technical approaches, photovoltaic sources placed in a distributed architecture supplying a high DC voltage HVDC bus points large advantages. Thus, after preliminary comparison of both solutions and concluding phases, this efficient solution finally constitutes the main original analysis presented in this contribution. The distributed PV structure is investigated, implemented and simulated in an original way under the OrCAD/Pspice software environment. The adaptation stage for maximum power transfer is modelled in detail. A method to calculate the optimal duty cycle for optimal use of PV panels power is proposed, tested and validated by the use of a marketed PV module datasheet

Monoclinic superstructure in the orthorhombic Ce10W22O81 from transmission electron microscopy

International audienceA complex rare earth tungstate structure, present in a two-phased powder, was solved by electron diffraction, precession and high resolution electron microscopy. The orthorhombic space group Pbnm and the atomic positions deduced from X-rays diffraction experiments were confirmed for Ce10W22O81. A C2/c monoclinic superstructure, with cell parameters a = 7.8 Å, b = 36.1 Å, c = 22.2 Å and β = 100.2°, was evidenced and attributed to a partial oxidation of Ce3+ leading to interstitial oxygen ions

Room temperature electronic template effect of pre-structured SmSi(111)-8x2 interface yielding self-aligned organic molecules

International audienceThis work describes an innovative concept for the development of organized molecular systems thanks to the template effect of the pre-structured semi-conductive SmSi(111) interface. This substrate was selected because Sm deposition in the submonolayer range leads to a 8x2-reconstruction, which is a well-defined one-dimensional semi-metallic structure. Adsorption of aromatic molecules (1,4-di-(9-ethynyltriptycenyl)-benzene) on SmSi(111)-8x2 and Si(111)-7x7 interfaces has been investigated by scanning tunneling microscopy (STM) at room temperature. Density functional theory (DFT) and semi-empirical (ASED+) calculations have been performed to define the nature of the molecular adsorption sites of the target molecule on SmSi as well as their self-alignment on this interface. Experimental data and theoretical results are in good agreement

Carbon nanotubes/ceria composite layers deposited on surface acoustic wave devices for gas detection at room temperature

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BAW Resonator as Elastic Characterization Tools of WO3 Thin Films

1st International Conference on Advances in Functional Materials (AFM), Stony Brook Univ, Stony Brook, NY, JUN 29-JUL 03, 2015International audienceWe report the elastic properties of tungsten trioxide WO3 films of various thicknesses using the dispersion behaviour of Balk Acoustic Wave BAW. Quartz crystal microbalance as well as BAW resonators are used for this purpose, allowing for the derivation of a reliable data set. WO3 films were characterized using X-ray diffraction, atomic force and scanning electron microscopy. The diffraction pattern showed crystallized layers with a pseudo cubic phase. The measured piezoelectric coefficient allowed fitting the model constants and obtaining the elastic coefficients and mass density. (C) 2016 Elsevier Ltd. All rights reserved

Morphological and structural investigation of SrWO 4 microcrystals in relationship with the electrical impedance properties

International audienceIn this paper, strontium tungstate (SrWO4) microcrystals have been synthesized at room temperature using a wet chemical method, without any surfactant or template, by adjustment of the precursor concentration and pH solution. The developed mineralization process allows obtaining homogeneous structures with controlled morphologies, including spindles and spheres. Scanning electron microscopy, X-ray diffraction combined with Rietveld analyses and Raman spectroscopy, are used to characterize the detailed scheelite-type tetragonal structures and morphologies and to highlight the size and microstrain effects. In addition to the Raman bands characteristic of the scheelite phase, it was found a strong low frequency modes assigned to high distortion of the SrO8 polyhedra. The mechanisms underlying growth and shape evolution are proposed taking into account the effects of precursor concentration and thermal treatment on the stability of the different morphologies which have been investigated in detail. Electrical conduction analyses have been carried out as a function of temperature in both AC and DC current modes. The results are interpreted in terms of a Nyquist representation, such that the spindles show a single semicircle at high frequencies, while a second semicircle appears at lower frequencies for the spheres. The measured conductivities have similar electrical transitions. Below 500 degrees C, the conductivity is mainly due to electron charge carriers; however above this temperature, the conductivity becomes mixt due to the order-disorder transition. Moreover, the associated activation energies of the spheres are higher than those of the spindles

Shape dependence of photosensitive properties of WO3 oxide for photocatalysis under solar light irradiation

International audienceTwo morphologies of nanostructured WO3, nanoplatelets (NP) and pseudospheres (PS), were synthesized using a simple chemical route. The obtained powders were structurally characterized using thermal analyses and a combined XRD with Rietveld refinement. Their morphological and growth mechanisms were followed by SEM during the maturation phase. The results showed a square/rectangular shape and pseudospherical morphology, which exhibited a monoclinic phase after calcination at 400 degrees C and an orthorhombic phase after calcination at 500 degrees C. The temperature treatment induced an increase of grain size for the NP lateral size, while the PS size remains temperature independent. The photocatalytic activity was evaluated by the degradation of methylene blue under solar light irradiation. The degradation process was investigated by studying the photosensitive properties, optical absorption, photoluminescence and photoresistance. The photodegradation activity of methylene blue is composed of a rapid and strong adsorption step followed by a photoinduced catalytic process. The PS sample revealed a higher adsorption rate than NP powders at the low calcination temperature, while the photoinduced catalysis is better at the high calcination temperature, reaching 88% at 500 degrees C. The photosensitive properties showed a low luminescence intensity and a long charge carrier recombination time, thus indicating the photocatalytic efficiency of the elaborated samples