64 research outputs found
Hole and Electron Contributions to the Transport Properties of Ba(Fe_(1-x)Ru_x)_2As_2 Single Crystals
We report a systematic study of structural and transport properties in single
crystals of Ba(Fe_(1-x)Ru_x)_2As_2 for x ranging from 0 to 0.5. The isovalent
substitution of Fe by Ru leads to an increase of the a parameter and a decrease
of the c parameter, resulting in a strong increase of the AsFeAs angle and a
decrease of the As height above the Fe planes. Upon Ru substitution, the
magnetic order is progressively suppressed and superconductivity emerges for x
> 0.15, with an optimal Tc ~ 20K at x = 0.35 and coexistence of magnetism and
superconductivity between these two Ru contents. Moreover, the Hall coefficient
RH which is always negative and decreases with temperature in BaFe2As2, is
found to increase here with decreasing T and even change sign for x > 0.15. For
x_Ru = 0.35, photo-emission studies have shown that the number of holes and
electrons are similar with n_e = n_h ~ 0.11, that is twice larger than found in
BaFe2As2 [1]. Using this estimate, we find that the transport properties of
Ba(Fe_0.65Ru_0.35)_2As_2 can be accounted for by the conventional multiband
description for a compensated semi-metal. In particular, our results show that
the mobility of holes is strongly enhanced upon Ru addition and overcomes that
of electrons at low temperature when x_Ru > 0.15.Comment: new version with minor correction
Influence de la teneur en oxygĂšne sur la microstructure et le comportement mĂ©canique de la phase « ex bĂȘta » rĂ©sultant de l'oxydation Ă haute tempĂ©rature (1000-1200°C) du zircaloy 4
International audienceL'Ă©tude ici illustrĂ©e s'intĂ©resse au comportement thermo - mĂ©tallurgique - mĂ©canique des alliages de Zr des tubes de gainage du combustible des RĂ©acteurs nuclĂ©aires Ă Eau PressurisĂ©e (REP), lors de transitoires Ă hautes tempĂ©ratures (HT) en ambiance vapeur d'eau, simulant des conditions hypothĂ©tiques accidentelles (dites APRP). Il apparaĂźt intĂ©ressant d'approfondir la connaissance des phĂ©nomĂšnes mĂ©tallurgiques et thermomĂ©caniques mis en jeu lors de tels transitoires, en particulier vis-Ă -vis du comportement mĂ©canique rĂ©siduel « post oxydation trempe ». DiffĂ©rentes teneurs en oxygĂšne ont Ă©tĂ© incorporĂ©es dans l'alliage Ă©tudiĂ©, pour simuler la diffusion de cet Ă©lĂ©ment dans le substrat mĂ©tallique qui intervient lors de l'oxydation HT. Des caractĂ©risations microstructurales par EBSD, MET, MEB... et des caractĂ©risations mĂ©caniques par essai de traction, mesures de constantes physiques... ont permis de dĂ©crire la microstructure et le comportement mĂ©canique de la phase rĂ©siduelle la plus ductile â phase dite « ex-bĂȘta » - rĂ©sultant de l'oxydation HT des gaines en zircaloy-4
A multifactorial approach including tumoural epidermal growth factor receptor, p53, thymidylate synthase and dihydropyrimidine dehydrogenase to predict treatment outcome in head and neck cancer patients receiving 5-fluorouracil
The prognostic value of tumoural epidermal growth factor receptor (EGFR), p53, thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) was analysed on 82 advanced head and neck cancer patients (71 men, 11 women; mean age 59). Induction treatment was cisplatinâ5-FU ± folinic acid (61 patients, Chem group) or concomitant cisplatinâ5-FUâradiotherapy (21 patients, RChem group). EGFR (binding assay), p53 protein (Sangtec immunoluminometric assay), TS and DPD activities (radioenzymatic assays) were measured on biopsies obtained at time of diagnosis. Significant positive correlation was demonstrated between p53 and EGFR. In the RChem group, p53 was higher in non-complete responders (median 1.03 ng mgâ1) than in complete responders (median 0.08 ng mgâ1) (P = 0.057). Univariate Cox analyses stratified on treatment group showed that specific survival (33 events) was significantly related to T staging, p53 taken as continuous or categorial (below vs over 0.80 ng mgâ1) variable, and EGFR (below vs over 220 fmol mgâ1); survival increased when EGFR and p53 were below thresholds. Multivariate stepwise analysis including T staging, EGFR and p53 revealed that T staging and EGFR were independent predictors of survival; relative risks were 3.68 for T staging and 2.65 for EGFR. Overall, EGFR remained an independent prognostic factor when response to treatment and T staging were considered in the multivariate analysis. © 1999 Cancer Research Campaig
An attempt to correlate ion irradiation behaviour and chemical durability of titanate- and zirconate-based ceramics
International audienceTitanate and zirconate samples from perovskite and pyrochlore families have been submitted to low energy heavy ion irradiation in order to pre-damage their crystalline structure. Samples irradiated below or near their amorphisation threshold were then leached in deionised water at 90 degrees C in static mode while samples irradiated above their amorphisation threshold were leached at 100 degrees C in dynamic mode. Below the amorphisation threshold, only slight effects of the pre-irradiation have been found on the chemical durability of titanate and zirconate from the perovskite family. Above the amorphisation threshold, perovskite surfaces exhibit a stronger hydration and an increase of the growth kinetics of secondary phases identified as TiOOH and ZrOOH compounds mainly. The pre-irradiated pyrochlore (Nd(2)Zr(2)O(7)) exhibits both a higher hydration degree and a higher Nd-Zr surface co-enrichment due to the destabilization of their network by the pre-irradiation. (C) 2008 Elsevier B.V. All rights reserved
Ion beam irradiation of Sn films deposited on YSZ(100)
International audienceThis paper reports the formation processes of crystalline Sn nanostructured films grown under ultra high vacuum conditions on monocrystalline yttria-stabilized zirconia (YSZ) substrates with (10 0) orientation. The microstructure of the films was analyzed using SEM and X-ray diffraction. Evaporation of Sit films yields crystallographically well-defined metallic islands of different shapes depending on the substrate temperature. The overall growth mechanism appears to follow the Stranski-Krastanov type. Irradiation of deposited films was performed at room temperature with 4 MeV Au2+ ions at a fluence of 10(15) cm(-2) to induce material decomposition and aggregation of host atoms. X-ray diffraction and Rutherford backscattering spectrometry (RBS) experiments conducted on Sn films deposited on YSZ(l 00) prior to and after irradiation demonstrate that ion irradiation drives a structural phase transformation for Sri and Zr-rich compositions. The microstructural evolution upon ion irradiation was also examined by cross-sectional transmission electron microscopy (TEM). (C) 2008 Published by Elsevier B.V
Towards Simulation of Dislocation-Based Creep Mechanisms: Application to Oxide Dispersion Strengthening Steels
International audienc
Thermodynamic Assessment of the Fe-Te System. Part I: Experimental study
International audienceA thermodynamic description of the Fe-Te system needs to be developed in order to model internal corrosion by fission products in fuel pins of Generation IV nuclear reactors. In preparation for a thermodynamic assessment of the system, an experimental study has been performed in order to clarify some unknown or conflicting phase diagram data. New phase diagram data have been obtained using Differential Thermal Analysis and isothermal heat treatments followed by electron microscopy with EDS and WDS analysis. The DTA analysis revealed new phase boundary data, and confirmed a very steep Fe-rich liquidus, supporting the possibility of a liquid miscibility gap in the Fe-FeTe region. The analyses also confirmed the probable eutectoid reaction ' at 523 DC. The invariant arrests of the unknown phase were consistent with information available in literature, but the phase was not identified via XRD of samples at its postulated composition. However, metallography of the samples revealed an unexpected microstructure pertaining to the phase, which might be the phase, and is discussed in this paper. The monoclinic space group C2/ is proposed for the phase based on XRD. The collected data will be used together with that available in literature to perform a thermodynamic Calphad assessment in a subsequent paper
Rubans Ag/Bi 2212 préparés par alternance de dépÎts électrolytiques et de traitements thermiques
Nous avons synthétisé par alternance de dépÎts électrolytiques et de traitements thermiques des couches de Bi
2212 de d'Ă©paisseur sur les deux faces de rubans d'argent de d'Ă©paisseur. GrĂące Ă une succession
de fusions partielles, la composition moyenne de nos couches s'homogénéise bien que les précurseurs soient
déposés de façon séquentielle. Comme dans le procédé classique connu sous le vocable "partial melt growth",
nous fondons nos précurseurs mais vue leur faible épaisseur au lieu de les refroidir trÚs lentement, nous ne les
maintenons que briÚvement dans l'état fondu, puis nous les trempons jusqu'à la température ambiante. Nous
synthétisons alors la phase Bi 2212 sans repasser au-dessus de son point de fusion. Afin
d'optimiser le procédé,
nous avons caractérisé la microstructure de nos échantillons à chacune des étapes de leur élaboration. Nous
présentons dans cet article la comparaison entre le procédé classique de fusion partielle et le nÎtre, ainsi que la
corrélation entre les traitements thermiques et les propriétés électriques. Au stade actuel de
l'optimisation,
nous préparons de façon reproductible des échantillons présentant une densité de courant critique de transport
d'environ 30 000 A/cm2 Ă 77 K et 300Â 000Â A/cm2 Ă 4,2 K, ce qui correspond Ă des courants de transport de
respectivement 6,3 et 63 AmpĂšres pour des Ă©chantillons de 3 mm de large, avec un rapport substrat sur supra de
7. Nous avons de plus vérifié que le courant critique était proportionnel à la largeur de l'échantillon, conduisant
à un courant critique de 42 A à 77 K et 100 A à 63 K pour les échantillons les plus larges que nous ayons testés
(20 mm)
Nanoscale characterization and formation mechanism of nanoclusters in an ODS steel elaborated by reactive-inspired ball-milling and annealing
International audienceReactive-inspired ball-milling is proposed as a new production route for oxide dispersion strengthened (ODS) steels. So a Feâ14Crâ2Wâ1Tiâ0.8Yâ0.2O (wt.%) ODS steel is elaborated by ball-milling of FeCrWTi and YFe3 plus Fe2O3 powders instead of Y2O3 and then by annealing at 800 °C for 5 min. Characterizations by Electron Probe MicroAnalysis and Atom Probe Tomography (APT) are performed after milling and after annealing. For the very first time, nanoclusters are observed after ball-milling by APT. Those nanoclusters are enriched in titanium, yttrium and oxygen and their mean radius is 0.8 nm. With annealing, the mean radius rises up to 1.4 nm and the number density as well as the enrichment factor in O, Ti and Y increase. So a new formation mechanism of nanoclusters is observed in those conditions of synthesis: ball-milling initiates the nanoclusters nucleation and during annealing, nucleation continues, accompanied by a slight growth of nanoclusters. Thus reactive-inspired ball-milling appears as a promising route for synthesizing ODS steels with a fine and dense dispersion of oxides
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