Formation Process of Hydrogen-Induced Amorphous RNi₂H_x (R=Sm, Gd, Dy, Er) Alloys

Abstract

The formation process of a hydrogen-induced amorphous phase in the C15 Laves phases, RNi₂H_x (R=Sm, Gd, Dy, Er) has been examined by X-ray diffraction and differential scanning calorimetry as a function of hydrogenation time. It has been demonstrated that there are two kinds of amorphization processes. That is, the amorphization in SmNi₂ and DyNi₂ compounds progresses by the nucleation and growth of a hydrogen absorbed amorphous phase. On the contrary, in GdNi₂ and ErNi₂ a hydrogen absorbed compound transforms polymorphously to the amorphous ones with increasing time. The JMA plot for the process of amorphization gives the numerical exponent n=3.9 for DyNi₂ and n=0.5 for GdNi₂, respectively. The difference in the process of hydrogen-induced amorphization in these alloys is discussed.