Hydrogenation behavior of the solid solutions RE4NiMg1−xAlx and RE4−yNiMg1+y with RE = Gd and Y

The solid solutions RE4NiMg1−xAlx (0 < x < 0.9) and RE4−yNiMg1+y (0 < y < 0.5) with RE = Gd and Y were synthesized from the elements in sealed tantalum ampoules in an induction furnace. The limit of solubility was established in both cases. All the samples crystallize with the cubic Gd4RhIn type structure, space group F-43m. The solubility is much lower in the case of Y than for Gd which is linked with steric effects. The hydrogen sorption is irreversible and the large exothermicity of the reaction can lead to the decomposition of the compounds into rare earth hydrides and metallic Ni and Mg. Nevertheless, it is shown that the Y based compounds can absorb almost 3 wt.% of hydrogen at room temperature and under moderate pressure. Furthermore, the solid solutions do not allow destabilization of the hydrides.