Elastic Recoil Detection Analysis

International audienceAmong the family of Ion Beam Analysis techniques for material characterization, Elastic Recoil Detection Analysis (ERDA) exploits the spectroscopy of recoil nuclei moving under the impact of the ions of the beam. This technique is well suited to light elements profiling, especially for hydrogen measurements which can be performed with usual helium-4 beams available in most facilities. This chapter presents an overview of ERDA main features and focuses on a selection of recent papers dealing with hydrogen measurements in materials for miscellaneous applications, divided into four sections: metals, ceramics, minerals, and thin films

Exploring the electrochemical behavior of InSb as negative electrode for Mg-ion batteries

International audienceMagnesium metal has a tendency to react with conventional electrolytes to form a barrier on its surface[1], rendering cations exchange impossible, and thus dramatically limiting reversible stripping/deposition of Mg. Unlike Mg metal, alloys based on p-block elements (Sn, Sb, In, Pb, Bi) do not appear to suffer from the formation of a blocking passivation layer in conventional electrolytes. These substitute electrodes appear therefore as a promising solution to overcome the problem of compatibility with electrolytes, even if the reaction mechanisms behind their operation in conventional electrolytes are still unsolved. In order to improve the performance of these electrodes, we evaluated a possible synergy effect between p-block elements, as already shown for SnSb[2] and BiSb[3]. We chose to work on InSb that may combine the high theoretical capacity of Sb and the lowest working potential reported for In. InSb, synthetized by ball-milling, shows an electrochemical behavior (Figure 1) drastically different from those of the lone elements. We will demonstrate that the combination of In and Sb is beneficial as it promotes the reactivity of Sb, similarly to BiSb alloy[3]. Structural and morphological ex situ characterization will also be described in details and correlated with the peculiar electrochemical behavior of InSb. Figure 1: Voltage profile of an InSb-based electrode cycled at a rate of C/100 in an electrolyte based of EtMgCl and Et2AlCl in THF

Impact of Spark Plasma Sintering Conditions on Ionic Conductivity in La1.95Sr0.05Zr2O7-δ Electrolyte Material for Intermediate Temperature SOFCs

International audienceSolid Oxide Fuel Cells (SOFC) have attracted much attention as potential energy source. Their high operating temperatures (800°C-1000°C) can lead to thermal, mechanical and chemical problems such as densification of electrodes or formation of an insulating layer at the electrode/electrolyte interface by interdiffusion [1-2]. To overcome these drawbacks, the Proton Ceramic Fuel Cell (PCFC) technology was developed. This technology, where the electrolyte is an H+ ion conductor in the form of ceramic oxide material, exhibits the intrinsic benefits of proton conduction in Polymer Exchange Membrane Fuel Cells (PEMFC) and the advantages of the SOFC technologies. Since the discovery of high temperature protonic conductivity in cerates [3-4], many investigations about pyrochlore-type proton conductors are performed [5-6]. These systems are characterized by mixed valence oxides (often rare earth) and anion vacancies as primary lattice defects. Under wet atmosphere, the proton conduction occurs via the hydration of oxygen vacancies after the material is exposed to a vapour-containing atmosphere according to the following equation 1 (inserted as part of the image file).     The conventional route for the preparation of lanthanum zirconate pyrochlore (LSZO) via solid-state reactions requires multiple milling and high temperature calcination steps. Also, this method leads generally to an heterogeneity of the final product, whereas wet chemical route, which consists of mixing precursors in a solution, could improve compositional homogeneity and stoichiometry. In this work, we have synthesized nano-sized La1,95Sr0,05Zr2O7-d using an oxalic co-precipitation method. As impedance spectroscopy measurements require high densification, only spark plasma sintering (SPS) gives dense materials. Other sintering processes such as hot isostatic pressing induce a segregation of strontium at the surface of the pellet[7],and thereby decrease proton conductivities. LSZO powders were densified using SPS apparatus under different sintering conditions: holding time, temperature and pressure. To maintain the same compacity for different grain sizes, starting powder materials were calcined at different temperatures in order to increase of the particle size. Thus several pellets with either different relative densities or grain sizes were obtained. The grain size increases with increasing of the sintering temperature. The proton conductivity behavior of those pellets was investigated by AC impedance spectroscopy under dry and wet atmospheres. The data were measured in the frequency range 0.1Hz – 6 MHz (Materials mates M2-7260 impedance analyzer) at intermediate temperatures 400-600°C. In order to verify the dependence of total resistance and capacitance, a DC-bias (UDC from 0 to 1V) was applied. The Nyquist diagrams were modeled by equivalent circuits based on resistors and constant phase elements (CPEs).  The ionic conductivities are clearly dependent on grain sizes (see Figure 1). In order to elucidate this dependence, it will be necessary to assess a porosity correction equation. The activation energies, calculated using the Arrhenius equation, increase with increasing grain sizes. The proton conductivities are higher in wet atmosphere than dry atmosphere. For example, the ionic conductivities of 120 nm-LSZO are 2.45 × 10-5 S.cm-1 and 3.30 × 10-5 S.cm-1 under dry and wet atmosphere (5% H2O) at 600°C, respectively. Figure 1 - Nyquist plots of impedance spectra for LSZO with different particle sizes at 600°C References[1]      S.C. Singhal, Solid State Ion. 135 (2000) 305. [2]      C. Xia, W. Rauch, F. Chen, M. Liu, Solid State Ion. 149 (2002) 11. [3]      F. Chen, O.T. Sørensen, G. Meng, D. Peng, J. Mater. Chem. 7 (1997) 481. [4]      H. Iwahara, H. Uchida, K. Ono, K. Ogaki, J. Electrochem. Soc. 135 (1988) 529. [5]      K.E.J. Eurenius, E. Ahlberg, C.S. Knee, Dalton Trans. 40 (2011) 3946. [6]      T. Shimura, M. Komori, H. Iwahara, Solid State Ion. 86–88, Part 1 (1996) 685. [7]      D. Huo, D. Gosset, G. Baldinozzi, D. Siméone, H. Khodja, B. Villeroy, S. Surblé, Solid State Ion. (submitted)

Surface blistering and flaking of sintered uranium dioxide samples under high dose gas implantation and annealing

International audienceHigh helium contents will be generated within minor actinide doped uranium dioxide blankets which could be used in fourth generation reactors. In this framework, it is essential to improve our understanding of the type of damage which a pellet could incur as a result of extensive helium build-up. This paper is an attempt at tackling this issue. Sintered uranium dioxide disks have been implanted with helium ions then annealed at various temperatures. Above a concentration of 0.4 at.% and above 1000°C, optical images of the sample surface revealed swollen grains and extensive areas which have exfoliated. Nuclear reaction microanalyses and atomic force microscopy observations were performed to demonstrate that helium has substantially precipitated within the swollen grains. Massive precipitation of the gas leads under these conditions to sample surface blistering which appears to precede flaking. Deuterium ion irradiations have also been performed at ambient and a direct flaking of the sample surface was observed, but for this phenomenon to be observed required much higher doses than in the He study, indicating that temperature could be an essential ingredient for gas to migrate and cause extensive precipitation. Such phenomena could possibly lead to degradation of the fuel

LES FAISCEAUX D'IONS : DE LA PHYSIQUE DES PLASMAS AUX APPLICATIONS DANS LES DOMAINES DE L'ANALYSE ET DE L'IRRADIATION

Ce travail est caractérisé par le fait qu'il se situe à la frontière entre technologie et recherche plus fondamentale. Le mémoire est organisé en 6 parties. Dans le chapitre 2, je donne un aperçu du travail mené dans le cadre du co-encadrement d'une thèse au sein de mon 1er laboratoire d'accueil, au CEA/Grenoble, dont l'objectif était de déterminer la distribution des populations ioniques dans un plasma de source ECR. Au chapitre 3, après avoir très brièvement rappelé les principes et techniques de l'analyse par faisceaux d'ions, je présente quelques caractéristiques de la microsonde nucléaire du CEA/Saclay en précisant ses spécificités. Le chapitre 4 donne quelques illustrations des applications dans le domaine des sciences des matériaux auxquelles j'ai participé au fil du temps. Les applications dans le domaine de la biologie, que j'ai contribué à développer au sein du laboratoire sont présentées au chapitre 5. Un développement important que j'ai mené sur la microsonde, ici à visée d'irradiation, est présenté au chapitre 6. Le chapitre 7 ouvre les perspectives de recherche qui me semblent intéressantes à développer dans les années à venir

Les éléments légers vus par microsonde nucléaire: applications pour les Sciences de la Terre

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Exploration d’alliages comme électrodes négatives de batteries Mg-ion

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Détection à très grand angle solide: Application à la NRA

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Unexpected behavior of InSb alloy for Mg-Ion batteries: unlocking the reversibility of Sb

International audienceElectrochemical behavior and performance of negative electrodes in metal batteries can be modified and improved by combining different elements. Herein, a beneficial coupling of In and Sb in the alloying reaction with Mg was considered through the preparation of the InSb alloy by mechanochemical synthesis. Despite a strong inactivity of Sb as a sole element in Mg-ion batteries, the combination of Sb with In partially unlocks the reversibility of the alloying reaction of Sb with Mg to form Mg3Sb2. For the first time, this beneficial effect is not only observed during the first magnesiation but along few tens of cycles. The analysis of the behavior of InSb through electrochemical and X-ray diffraction measurements also revealed a more complex path than reported in the literature. Uncommonly a preferential electrochemically-driven amorphization of MgIn is suggested in standard galvanostatic measurements. Crystallization of MgIn is however observed through a galvanostatic intermittent titration technique, suggesting strong kinetic effects on the microstructure, strain or disorder in the InSb phase upon magnesiation

Ion beam analysis in extreme environment: investigation of radioactive samples at the micrometric scale

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