Crystal structures and hydrogenation characteristics of Ca8(Al1−xNix)3 alloys

The phase relations and hydrogenation characteristics of the Ca8(Al1−xNix)3 (x=0, 0.1, 0.2, 0.3 and 0.4) alloys were studied. It was found that the maximum solid solubility of Ni in the Ca8Al3 phase is about x=0.09. In the Ni-substituted Ca8(Al0.91Ni0.09)3 phase, the Ni atoms occupy the Al sites but the occupation factor of Ni in 1c site is larger than that in 2i site. The lattice parameters of the Ca8Al3 phase have no obvious change after the partial substitution of Al by Ni because of the small solid solubility of Ni. However, further increasing x leads to a decrease in the amount of the Ca8Al3 phase and an increase in the amount of Ca and NiAl. When x=0.4, the Ca8Al3 phase disappears entirely and only the NiAl phase and the Ca-based solid solution with a solid solubility of about 0.05 at.% Al exist in the alloy. Both the binary Ca8Al3 phase and the Ni-substituted Ca8Al3 phase can be hydrogenated into CaH2 and Al at 473 K, but the former shows a slower hydrogenation reaction than the latter.