Distribution of hydrogen in metal hydrides studied by in situ powder neutron diffraction

摘要

Interstitial metal hydrides were studied by in situ powder neutron diffraction for their use in hydrogen storage. The main focus was the distribution of hydrogen atoms in the materials. In full hydrides of LaNi_(5-x)Al_x, hydrogen occupation depended strongly on the amount of Al. The symmetry varied from P6_3mc (x=0) to P6mm (x=0.1) and P6/mmm (x≥0.25) with change in occupancy of each site. Variation in hydrogen occupation during absorption and desorption was analyzed for LaNi_(4.78)Sn_(0.22) Redistribution between three tetrahedral sites was observed during desorption. La_5Ni_(19)-based hydrides with a structure consisting of stacking La_2Ni_4 and LaNi_5 cells were also studied. Rietveld refinement of La_4MgNi_(19)D_(24) showed that hydrogen distributed almost evenly in LaMgNi_4 and LaNi_5 cells (0.8-1.0 H/M). which was consistent with the uniform lattice expansion of those cells. This result indicated that substitution of Mg for La changed the preferred sites for hydrogen occupation in the La_2Ni_4 and LaNi_5 cells.