Crystal structures and hydrogenation-dehydrogenation characteristics of Er(Ni1−xMnx)2

The crystal structures and hydrogenation-dehydrogenation characteristics of Er(Ni1−xMnx)2 compounds are investigated in this work. It is found that either annealing or hydrogenation leads to ordering transition of ErNi2 from MgCu2-type structure to TmNi2-type superstructure. As Mn content is within x = 0.2-0.8 and 0.9-1, Er(Ni1−xMnx)2 compounds have C15 and C14 structures, respectively. The hydrogen absorption content of the C15-type Er(Ni1−xMnx)2 increases with raising Mn content x, however, the absorption plateau pressure decreases gradually and hydrogen desorption becomes difficult. ErMn2 can absorb hydrogen to form irreversible ErMn2H3.4 and reversible ErMn2H4.8 at 3.5 × 10−5 and 1.5 × 10−1 MPa, respectively. Nevertheless, the C14-type Er(Ni0.1Mn0.9)2 compound is subjected to decomposition into ErMn2Hz and ErNi2Hy during hydrogen absorption.