Structural studies of pseudobinary La(Cu1−xNix)2 compounds and their hydrides

The effect of Cu-for-Ni substitution on the structural and hydrogenation properties of the LaCu2 compound with hexagonal AlB2 type structure has been studied. An extended solid solution was found from LaCu2 to La(Cu0.35Ni0.65)2. The La(Cu1−xNix)2 compounds easily absorb hydrogen at room temperature under 1 bar pressure, after preliminary activation treatment by heating in vacuum. Hydrogenation of LaCu2 resulted in the formation of amorphous LaCu2H3.3 hydride. For all Ni-substituted compounds formation of crystalline hydrides with CeCu2 or AlB2 type structure of the metallic sublattice and hydrogen content up to 4.4 at.H/f.u was observed. As found, long-term exposure of the La(Cu0.4Ni0.6)2H4.2 and La(Cu0.35Ni0.65)2H4.0 hydrides to the air or their heating under vacuum up to 100 °C is accompanied by structural transition of the metallic sublattice to Fe2P type structure, previously observed for Pr(Cu,Ni)2-based hydrides.