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 La
2Ni
7- and La
5Ni
19-based hydrides with stacking structures consisting of La
2Ni
4 cells and LaNi
5 cells. La
2Ni
7 formed two hydrides, La
2Ni
7H
7.1 and La
2Ni
7H
10.8. During formation of La
2Ni
7H
10.8, La
2Ni
4 and LaNi
5 cells expanded by 69.8% and 12.2%, respectively, indicating that most of absorbed hydrogen was located in La
2Ni
4 cells. In contrast, La
5Ni
19-based La
4MgNi
19 formed only one hydride, La
4MgNi
19H
∼24. Hydrogen was distributed almost evenly in LaMgNi
4 and LaNi
5 cells (0.8-1.0 H/M) in La
4MgNi
19D
∼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 La
2Ni
4 and LaNi
5 cells, which leads to difference in hydrogenation properties.
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