Homogeneity range and crystal structure of Ni substituted Mg6(Pd,Ni) complex intermetallic compounds

The solubility of nickel in Mg6Pd compound has been studied by chemical and structural methods. The solubility limit at 673 K attains 9 at% Ni, i.e. more than four times the value previously reported. Therefore, a re-determination of the ternary Mg-Pd-Ni phase diagram in the Mg-rich corner is desirable. Mg6(Pd,Ni) compounds have the same crystal structure as the binary Mg6Pd compound. The unit-cell composition at the solubility limit is Mg344(2)Pd12(1)Ni36(1) with 75% of Ni atoms substituting Pd ones. Ni substitution occurs on the three crystallographic sites exclusively occupied by Pd in Mg6Pd. The substitution is not fully random. Ni atoms have a slight preference for site with low coordination number. The results reported here enlarge the compositional range in which Mg6(Pd,Ni) compounds can be used as reversible hydrogen storage materials.