Groupe dEtude de la Matiere Condensee

Martigné-Briand, France

Groupe dEtude de la Matiere Condensee

Martigné-Briand, France
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Lin X.,University Pierre and Marie Curie | Gourgout A.,University Pierre and Marie Curie | Gourgout A.,CEA Grenoble | Bridoux G.,University Pierre and Marie Curie | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We present a study of thermal conductivity in superconducting SrTi1-xNbxO3, sufficiently doped to be near its maximum critical temperature. The bulk critical temperature, determined by the jump in specific heat, occurs at a significantly lower temperature than the resistive Tc. Thermal conductivity, dominated by the electron contribution, deviates from its normal-state magnitude at bulk Tc, following a Bardeen-Rickayzen-Tewordt behavior, which is expected for thermal transport by Bogoliubov excitations. The absence of a T-linear term at very low temperatures rules out the presence of nodal quasiparticles. On the other hand, the field dependence of thermal conductivity points to the existence of at least two distinct superconducting gaps. We conclude that optimally doped strontium titanate is a multigap nodeless superconductor. © 2014 American Physical Society.

Deulkar S.H.,National Cheng Kung University | Huang J.-L.,National Cheng Kung University | Neumann-Spallart M.,Groupe dEtude de la Matiere Condensee
Journal of Electronic Materials | Year: 2010

Pulsed laser deposition was used to produce thin films of zinc oxysulfide (ZnO xS 1-x) on quartz substrates. The target was a sintered pellet (ZnO 0.39S 0.61) made of a solution precipitate. The film composition obtained by electron probe microanalysis (EPMA) was ZnO 0.41S 0.59, ZnO 0.44S 0.56, and ZnO 0.37S 0.63 for substrate temperatures of 450°C, 540°C, and 630°C, respectively. X-ray diffraction (XRD) showed that samples deposited at 450°C and at 540°C had a prominent cubic sphalerite phase, whereas samples deposited at 630°C consisted of three phases, viz. hexagonal wurtzite and cubic sphalerite (ZnS), and hexagonal zincite (ZnO). With respect to the tabulated lattice spacings for sphalerite (cell constant 0.5406 nm), distinct shifts were observed for the low temperature samples, yielding cell constants around 0.533 nm. Transmission electron microscopy (TEM)-selected area electron diffraction studies support the XRD data. Patterns of films deposited at 540°C could be indexed as sphalerite, with similar lattice shifts as in XRD, resulting in a cell constant of 0.53. Locally highly resolved chemical analysis by TEM-energy dispersive x-ray analysis revealed a stoichiometry that was consistent with the EPMA results. Ultraviolet (UV)-visible transmission measurements of the films led to bandgap energies around 3.3 eV, which is well below the reported bandgap energies of ZnS. © 2010 TMS.

Perrin S.,CEA Saclay Nuclear Research Center | Marchetti L.,CEA Saclay Nuclear Research Center | Duhamel C.,MINES ParisTech Center of materials | Sennour M.,MINES ParisTech Center of materials | Jomard F.,Groupe dEtude de la Matiere Condensee
Oxidation of Metals | Year: 2013

Oxidation of stainless steel in PWR primary water at 325 C was studied by investigating the influence of defects created at the alloy subsurface by proton irradiation before corrosion exposure. Corrosion experiments were conducted by sequentially exposing samples, with H 2 18 O used for the second exposure. The oxide layer, formed in these conditions was studied by SEM and TEM and could be divided in two parts: an external discontinuous layer composed of crystallites rich in iron and an internal continuous layer richer in chromium. Tracer experiments revealed that the growth of this protective scale was due to oxygen diffusion in the grain boundary of the oxide layer. Defects created by irradiation have an effect on the two oxide layers. They are a preferential nucleation site for the external layer and so increase the density of the crystallites. They also induce a slower diffusion of oxygen in the internal layer. © 2013 Springer Science+Business Media New York.

Jambon F.,CEA Saclay Nuclear Research Center | Marchetti L.,CEA Saclay Nuclear Research Center | Marchetti L.,CEA Marcoule Nuclear Site | Sennour M.,MINES ParisTech Center of materials | And 2 more authors.
Journal of Nuclear Materials | Year: 2015

This study aims at characterizing the interactions of hydrogen with point defects and their clusters in nickel-based superalloys. For this, nickel ion implantation was used to create defects in the sub-surface of alloy 690 coupons. The interaction of hydrogen with these defects was studied thanks to SIMS depth profile analysis performed after deuterium cathodic charging, and different annealing treatment. In parallel, TEM observations were carried out in order to qualify and quantify the defects responsible for the trapping, and to observe their evolution in the presence of hydrogen. All the results exhibit a strong interaction of hydrogen with implantation-defects, up to high temperatures (325 °C). Also, hydrogen is shown to assist defects reorganisation, in a way similar to the effect of temperature. The effect of hydrogen on the alloy atoms as explored by SIMS, combined with the TEM investigation of defects evolution in the presence of hydrogen, allows to suggest that the main mechanism for hydrogen-assisted motion of defects is by lowering the lattice friction, thus decreasing the activation volume for the unfaulting or motion of point defect clusters, up to dislocation loops. © 2015 Elsevier B.V. All rights reserved.

Lefaix-Jeuland H.,CEA Saclay Nuclear Research Center | Moll S.,CEA Saclay Nuclear Research Center | Legendre F.,CEA Saclay Nuclear Research Center | Jomard F.,Groupe dEtude de la Matiere Condensee
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

Helium distribution in implanted monocrystalline and polycrystalline Fe samples has been measured by secondary ion mass spectrometry (SIMS). The use of Cs+ primary ions in conjunction with the detection of CsHe + molecular ions was shown to be an efficient method to overcome the very high first ionization potential of helium. The implantation ranges of 60 keV He ions in samples are measured about 220 nm in agreement with projected ranges calculated by TRIM. He concentrations at or above 5 × 10 18 at/cm3 (∼60 ppm) were measured. This study confirms the paramount interest of SIMS as a direct He depth profiling technique. © 2012 Elsevier B.V. All rights reserved.

Jambon F.,CEA Saclay Nuclear Research Center | Marchetti L.,CEA Saclay Nuclear Research Center | Jomard F.,Groupe dEtude de la Matiere Condensee | Chene J.,CNRS Laboratory for Analysis and Modelling for Biology and Environment
Solid State Ionics | Year: 2013

This study aims at providing quantitative data concerning the oxygen and hydrogen diffusion through the oxide scale formed on alloy 600 in PWR primary medium conditions (325 C) using 2D and 18O isotopes as markers. The diffusion coefficients were calculated according to a short-circuit diffusion of the tracers along the oxide grain boundaries (so-called "C-regime"). The values obtained are respectively Dsc = 4.6 +/- 0.9 × 10- 17 cm2/s for 18O, and Dsc = 5.2 +/- 1.2 × 10- 17 cm2/s for 2D. These experiments confirm that the transport mechanism of hydrogen through the oxide scale as hydroxide ions on the anionic sublattice is highly probable. The effect of hydrogen subsequent absorption by the alloy substrate, notably in stress corrosion cracking phenomenon is discussed. © 2012 Published by Elsevier B.V.

Neumann-Spallart M.,Groupe dEtude de la Matiere Condensee | Sadale S.B.,Groupe dEtude de la Matiere Condensee
Journal of New Materials for Electrochemical Systems | Year: 2010

Polycrystalline, monoclinic, uniform WO3 films of up to 2.5 μm thickness were prepared by drop casting onto F:SnO2/glass using as precursor peroxo-tungstic acid and polyethylene glycol in water, and firing in air at 520°C. Under illumination of such n-type semiconducting electrodes in junctions with aqueous electrolytes, photocurrents were produced. Under depletion conditions, IPCEs (incident photon to current efficiencies) of up to 0.7 at 365 nm and 0.2 at 405 nm were obtained. The photosensitivity extends into the visible with an onset at 470 nm. This opens the way for solar light powered electrochemical processes like pollutant degradation. The photocatalytic activity of such layers was examined using the azo-dye acid orange 7 (AO7) as a model pollutant. Degradation of 1 mM AO7 was carried out under backside UVA broadband illumination of electrodes of 62 cm2 active surface area, using a thin film flowthrough reactor equipped with a stainless steel counter electrode, rapid recirculation of the electrolyte, and electrical bias of 1.1 - 1.3 V. During illumination, the concentration of AO7 decreased with an apparent first order rate constant, k, of 1.44.10-4 s-1, corresponding to a specific decay constant of 2.3.10-7 -2 for a light intensity of 4.7.10-9 E.s -1cm-2. © J. New Mat. Electrochem. Systems.

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