The RENi4Ga (RE = Dy, Ho, Er) intermetallic compounds - Crystal structure and hydride properties

New ternary rare earth based intermetallic compounds of the composition RENi4Ga (RE = Dy, Ho, Er) were prepared and studied using X-ray powder diffraction. All compounds were found to be hexagonal and to crystallize in the space group P6/mmm with the CaCu5 type of structure, i.e., the same symmetry as their prototype binaries RENi5. The interaction with hydrogen was also studied. It was found that all intermetallics react readily and reversibly with hydrogen to form hydrides with hydrogen contents of up to 3.48 hydrogen atoms per alloy formula unit at room temperature. The entropy, the enthalpy and the Gibbs free energy of formation have been extracted from the equilibrium plateau in the pressure composition desorption isotherms. The thermodynamic parameters and the hydrogen capacity of the RENi4Ga-hydrogen systems are compared with the corresponding values for their aluminium analogues and briefly discussed