Synthèse et caractérisation d'hydrures d'éléments légers sous haute pression

Abstract : Over the past 5 years numerous calculations have unveiled a novel view on the chemical combination of hydrogen with metals under pressure. Three remarkable trends can be identified: (i) Hydrogen stoichiometry should drastically increase under pressure in metals, (ii) Polyhydrides with non-traditional stoichiometries should be stable under pressure, (iii) These hydrogen-dominant systems may become metallic at much lower pressure than for pure hydrogen and could exhibit a high-temperature of superconductivity. A systematic experimental study of different hydrides of low Z-elements has been undertaken in this thesis. First, a new synthesis method of high-quality and high-purity samples has been developed: a metallic foil is heated at high pressure in hydrogen medium using a YAG-laser. Using this method hydrides of aluminium (AlH3), beryllium (BeH2) and iron (FeHx) were synthesized at high pressure in a diamond anvil cell. These compounds were characterized in situ by means of Raman spectroscopy in our laboratory, infra-red spectroscopy and X-ray diffraction using synchrotron radiation light sources. Our results evidence that the properties of the hydrides are strongly influenced by the properties of the hydrogen sublattice and confirm the existence of a strong analogy between hydrides with a high hydrogen content and pure hydrogen. Moreover we confirmed the stability of new polyhydrides with non-traditional stoichiometries under high pressure through the synthesis of new iron hydrides FeH2 and FeH3 and the formation of LiH2 and LiH6 when compressing pure lithium hydride LiH.
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Submitted on : Thursday, September 24, 2015 - 10:53:00 AM
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Charles Pépin. Synthèse et caractérisation d'hydrures d'éléments légers sous haute pression. Physique [physics]. Ecole polytechnique, 2015. Français. ⟨tel-01204564⟩

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