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Impact de la nanostructuration sur la diffusion de l’hydrogène étudiée par une approche multi-échelle dans le matériau pyrochlore La₂Zr₂O₇ dopé Sr

Abstract : Due to the increase of energy demand and environmental issues of fossil energy, many researches are moving towards green energy. In this context, several technologies using hydrogen have been developed. To reduce the working temperature of SOFC fuel cell, the concept of PCFC is emerging. The ionic conductivity is due to hydrogen instead of oxide anions. The A₂B₂O₇ compounds are promising candidates as electrolyte materials for PCFC. However, it appears necessary to understand the hydrogen diffusion mechanisms in these materials before to investigate news materials with best properties. In this work, a multi-scale approach is performed to study the impact of microstructure on proton-conducting properties in Sr doped La₂Zr₂O₇ as model material. Several synthetic routes have been used to obtain powders with different morphologies.At the nanometric scale, studies by X-ray diffraction, then by Raman spectroscopy and electron energy loss spectroscopy (EELS) have shown that the low temperature structure were disordered a pyrochlore structure. The latter is ordered during thermal annealing. At the micrometric scale, ion beam techniques allowed us to get the hydrogen concentration profiles on the previously hydrated materials. The amount of incorporated hydrogen depends on the densification processes. At the macroscopic scale, impedance spectroscopy measurements were used to obtain information on the electrical behavior of materials. Evidence of proton conductivity has been demonstrated in wet atmosphere. This conductivity is highly dependent not only on the sample preparation but also on processes densification used.
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Da Huo. Impact de la nanostructuration sur la diffusion de l’hydrogène étudiée par une approche multi-échelle dans le matériau pyrochlore La₂Zr₂O₇ dopé Sr. Autre. Ecole Centrale Paris, 2015. Français. ⟨NNT : 2015ECAP0046⟩. ⟨tel-01297051⟩

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