The effect of aluminium on the structural and hydrogen sorption properties of ErNi5

The substitution of aluminium for nickel and its effect on the structural and hydrogen sorption properties of the binary ErNi5 has been studied. It was determined that nickel can be replaced by aluminium up to the composition ErNi,Al, without changing the prototype crystal structure of the CaCu5 type (space group P6/mmm). However, beyond this composition and up to ErNi2Al3 there also exists a ternary single phase region, with a structure of the YCo3Ga2 type, but closely related to the CaCu5 structure. It was found that all ternary alloys having the CaCu5 structure absorb between 1.96 and 2.95 hydrogen atoms per formula unit at room temperature. The binary ErNi5 as well as the remaining ternary alloys do not exhibit any significant hydrogen uptake. The structural and hydrogen sorption properties of the ErNi5-xAlx system are compared with some other related systems and briefly discussed. Generally, in these systems the hydrogen capacity and the equilibrium pressure decrease with increased content of aluminium. In the case of ErNi5-xAlx it was found that the hydrogen capacity increases and the equilibrium pressure decreases as the concentration of aluminium increases.