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

Abstract

Abstract The crystal structures and hydrogenation–dehydrogenation characteristics of Er(Ni 1− x Mn x ) 2 compounds are investigated in this work. It is found that either annealing or hydrogenation leads to ordering transition of ErNi 2 from MgCu 2 -type structure to TmNi 2 -type superstructure. As Mn content is within x = 0.2–0.8 and 0.9–1, Er(Ni 1 − x Mn x ) 2 compounds have C15 and C14 structures, respectively. The hydrogen absorption content of the C15-type Er(Ni 1 − x Mn x ) 2 increases with raising Mn content x , however, the absorption plateau pressure decreases gradually and hydrogen desorption becomes difficult. ErMn 2 can absorb hydrogen to form irreversible ErMn 2 H 3.4 and reversible ErMn 2 H 4.8 at 3.5 × 10 −5 and 1.5 × 10 −1 MPa, respectively. Nevertheless, the C14-type Er(Ni 0.1 Mn 0.9 ) 2 compound is subjected to decomposition into ErMn 2 H z and ErNi 2 H y during hydrogen absorption.