Solid solubility of Mg in Ca2Ni7 and hydrogen storage properties of (Ca2−xMgx)Ni7 alloys

The phase relations and hydrogen storage properties of the (Ca2−xMgx)Ni7 alloys were investigated. It was found that the maximum solid solubility of Mg in the (Ca,Mg)2Ni7 phase is about x = 0.5 in the present study. The ‘inter-block-layer’ type stacking faults exist in the (Ca,Mg)2Ni7 phase when Mg content is very low. However, the density of stacking faults decreases and the lattice parameters reduce as Mg content increases to its maximum solid solubility. Thus the (Ca1.5Mg0.5)Ni7 alloy has a good reversibility of hydrogen absorption–desorption.