A correlation between stability of compounds and structure of hydrogen-induced amorphous alloys in GdM 2 (M = Fe, Co, Ni)

Abstract

Enthalpy changes ΔH for hydrogen absorption and desorption, hydrogen-induced amorphization (HIA) in C15 Laves phases c-GdM 2 (M = Fe, Co, Ni) and crystallization of the resultant amorphous alloys a-GdM 2H x have been measured by differential scanning calorimetry (DSC). Furthermore, structures of a-GdM 2H x have been investigated by X-ray diffractometry (XRD) to correlate their structures with the stabilities of the original compounds. Both a-GdFe 2H 3.0 and a-GdCo 2H 3.4 prepared from the less stable compounds show the strong tendency for the same kinds of metal atoms to cluster and crystallize to GdH 2 and Fe(Co). Correspondingly, the sum of ΔH for all reactions become equal to that for the formation of GdH 2. On the contrary, a-GdNi 2H 3.5 prepared from the stable compound shows a rather homogeneous structure and crystallizes to GdH 2 and GdH 2 and GdNi 5. As a result, the sum of ΔH shows a large negative value in comparison with that for the formation of GdH 2.