Tb 2-x Nd x Zn 17-y Ni y (x = 0.5, y = 4.83): a new intermetallic with a maximum disordered structure and its hydrogen storage properties.

The ternary Tb 2-x Nd x Zn 17-y Ni y (x = 0.5, y = 4.83) disordered phase belongs to the structural family based on the rhombohedral Th 2 Zn 17 structure type. The structure is maximally disordered since all the sites are occupied by statistical mixtures of atoms. The Tb/Nd mixture of atoms occupies the 6c site (site symmetry 3m). The statistical mixtures Ni/Zn consisting of more Ni atoms are located in the 6c and 9d (symmetry .2/m) sites. In the following 18f (site symmetry .2) and 18h (site symmetry .m) sites are located Zn/Ni statistical mixtures which consist of more Zn atoms. Zn/Ni atoms form three-dimensional networks with hexagonal channels that fill statistical mixtures of Tb/Nd and Ni/Zn. The Tb 2-x Nd x Zn 17-y Ni y compound belongs to the family of intermetallic phases capable of absorbing hydrogen. In the structure, there are three types of voids, namely, 9e (site symmetry .2/m), 3b (site symmetry \overline{3}m) and 36i (site symmetry 1), in which hydrogen can be inserted, and the maximum total absorption capacity can reach 1.21 wt% H 2 . Electrochemical hydrogenation shows that the phase absorbs 1.03% of H 2 , which indicates partial filling of the voids with H atoms.