Hydrogen-induced phase transitions in RNi3 and RY2Ni9 (R = La, Ce) compounds

Structure stability of RNi3 and RY2Ni9 (R = La, Ce) during cycling of hydrogen absorption/desorption was investigated by both solid-H2 reaction and electrochemical measurements, in order to understand the mechanism responsible for the poor reversibility, and to reveal the differences between RNi3 and RY2Ni9 compounds. It has been found that, all of the cycled RNi3 and RY2Ni9 were subject to partial amorphization. This hydrogen-induced amorphization (HIA) occurred immediately in LaNi3, but proceeded gradually in CeNi3, LaY2Ni9 and CeY2Ni9. The HIA in these compounds is attributed to the RM2 subunits in their crystal structures.