水素吸蔵合金の水素吸蔵・放出反応に伴う構造変化のその場観察

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Interstitial metal hydrides for hydrogen storage were studied by in situ powder X-ray and neutron diffractions. This paper reports structural change and distribution of hydrogen atoms in La2Ni7- and La5Ni19-based hydrides with stacking structures consisting of La2Ni4 cells and LaNi5 cells. La2Ni7 formed two hydrides, La2Ni7H7.1 and La2Ni7H10.8. During formation of La2Ni7H10.8, La2Ni4 and LaNi5 cells expanded by 69.8% and 12.2%, respectively, indicating that most of absorbed hydrogen was located in La2Ni4 cells. In contrast, La5Ni19-based La4MgNi19 formed only one hydride, La4MgNi19H∼24. Hydrogen was distributed almost evenly in LaMgNi4 and LaNi5 cells (0.8-1.0 H/M) in La4MgNi19D∼24 from Rietveld refinement of in situ neutron diffraction data. This result indicated that Mg substitution for La changes preference of hydrogen occupation in the La2Ni4 and LaNi5 cells, which leads to difference in hydrogenation properties.