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Sur l'intercalation dans le graphite des alcalino-terreux et de l'europium en présence de lithium

Abstract : The immersion of pyrographite platelets in lithium based liquid alloys allows the intercalation of alkaline earth metals and europium in this host structure. This liquid-solid synthesis method led to the formation of graphite-Li-Ca and graphite-Li-Eu ternary compounds as well as bulk samples of the CaC6, BaC6 and EuC6 binaries. The study of the graphite-lithium-calcium system has made it possible to determine the formation mechanism of the phases CaC6 and Li3Ca2C6, which includes two stages systematically. The crystal structure of CaC6 has been fully resolved. This phase adopt a rhombohedral structure with the space group . Meanwhile, additional information has been provided to the crystal structure of Li3Ca3C6. The study of magnetic properties of CaC6 and Li3Ca2C6 indicates that these phases are superconductors with critical temperatures close to 11 K. An electrodynamics characterization, undertaken in order to identify the mechanism responsible of the superconductivity of CaC6, has shown that this compound appears to be a conventional superconductor. By using the synthesis method in molten alloy media, EuC6 binary compound and an original ternary phase were isolated during the study of the graphite-lithium-europium system. This ternary compound has along the axis an atomic stacking containing several sheets but with two main layers of europium. The lithium has however not been estimated, due to the experimental difficulty related to the determination of its amount. The chemical formula is then written LixEuC4. Magnetic measurements performed on this ternary compound reveal a complex behaviour below 225 K. Although the structure is not fully resolved, some simple geometric considerations associated with an analogy with the EuC6 compound can explain the magnetic behaviour of LixEuC4 qualitatively.
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  • HAL Id : tel-01748261, version 1



Nicolas Emery. Sur l'intercalation dans le graphite des alcalino-terreux et de l'europium en présence de lithium. Autre. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10059⟩. ⟨tel-01748261⟩



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