Super-hydrures sous pression pour le stockage de l’hydrogène et la supraconductivité : développement d’outils et résultats sur H3S, CrHx, LiBH4 et NaBHx.

Abstract : Recently, under pressures of several gigapascals, new hydrides have been synthesised with striking properties that may herald technological breakthroughs for hydrogen storage and superconductivity. In this PhD thesis, several superhydrides have been studied experimentally and simulated by DFT. The pressure phase diagrams of LiBH4 and NaBH4, two compounds of interest for hydrogen storage, have been explored thanks to X-ray diffraction and Raman and infrared spectroscopy up to pressures of 300 GPa without observing any decomposition. The insertion of hydrogen inside NaBH4 generates the superhydride NaBH4(H2)0.5. To refine the interpretation of the record superconductivity found in H2S under pressure at 200 K, the superhydride H3S has been synthesised from S and H elements. The results of the diffraction study seem to be at odds with the commonly accepted interpretation that Im-3m H3S is responsible for the superconductivity observed and leaves the door open to other interpretations. Finally, CrHx hydrides with x = 1, 1.5 and 2 have also been synthesised from the elements and characterised by X-ray diffraction. Although these hydrides do correspond to the ones that had been numerically predicted, the absence of the expected higher stoichiometries is discussed. To measure the superconductivity temperatures calculated for MHx hydrides, a miniature diamond anvil cell which allows the detection of a Meissner effect has been developed.
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Adrien Marizy. Super-hydrures sous pression pour le stockage de l’hydrogène et la supraconductivité : développement d’outils et résultats sur H3S, CrHx, LiBH4 et NaBHx.. Matière Condensée [cond-mat]. Université Paris-Saclay, 2017. Français. ⟨NNT : 2017SACLX115⟩. ⟨tel-01815284v2⟩

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