MgNi ₂ B ₆ as a new representative of the CeCr ₂ B ₆ structure type

The ternary boride MgNi₂B₆ (magnesium dinickel hexaboride) crystallizes as a new representative of the CeCr₂B₆ structure type. The Mg and Ni atoms occupy sites with mmm and mm2 symmetry, respectively. The B atoms occupy two sites with m.. and m2m symmetry. The 14-membered polyhedron around the Mg atom is a hexagonal prism, with two adjacent lateral faces centred by Mg atoms. The Ni atoms are encapsulated in 10-vertex polyhedra. The trigonal prismatic coordination is typical for both B atoms. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation (TB-LMTO-ASA) method. The electron concentration is higher around the B atoms, which form eight-membered channels along b, which are filled with Mg and Ni atoms. The maximum hydrogen absorption is up to 2.38 wt% H₂.