Structural characterization and some hydrogen absorption properties of (MgxCa1−x)Ni2.6: A new phase in the Mg-Ca-Ni system

A new structural type has been found for the compound with nominal composition (MgxCa1−x)Ni2.6. Its structure is made of nine layers (6 AB2 + 3 AB5) stacked in an original manner. The average structure may be regarded as a Gd2Co7 type-structure in which half of the AB5 blocks have been replaced by AB2 blocks. The hydrogen sorption properties are similar to those of the Ca0.4Mg0.6Ni3 compound with the PuNi3 structure. However, the resulting arrangement departs significantly from the PuNi3 structural type since a symmetry reduction from R-3m into R3 takes place.