A preliminary study of some “pseudo-AB2AB2” compounds: RENi4MgRENi4Mg with RE=LaRE=La, Ce and Gd. Structural and hydrogen sorption properties

The compounds RENi4MgRENi4Mg have been elaborated by mechanical alloying (MA) and a subsequent heat treatment at 600∘C for 1 h. The lattice parameters are in good agreement with those already reported: 7.165A˚ for LaNi4MgLaNi4Mg, 7.030 Å for CeNi4MgCeNi4Mg and 7.038A˚ for GdNi4MgGdNi4Mg. The hydrogen sorption behaviors are strongly influenced by the rare earth used: for La compound, hydrogen absorption leads to a structural change and no desorption can be observed, for Ce compound, no reaction towards hydrogen can be noticed and for Gd compound, hydrogen can be absorbed and desorbed reversibly at room temperature. Moreover, for GdNi4MgGdNi4Mg, no structural change is reported after hydrogenation and only a slight volume expansion can be noticed (e.g. 5%). The MA process has also been used successfully for the elaboration of GdNi4-xAlxMgGdNi4-xAlxMg up to x=1x=1. In these substituted compounds, hydrogen can also be absorbed and desorbed reversibly at room temperature.