A CORRELATION BETWEEN STABILITY OF COMPOUNDS AND STRUCTURE OF HYDROGEN-INDUCED AMORPHOUS-ALLOYS IN GDM2(M = FE, CO, NI)

Enthalpy changes DELTAH for hydrogen absorption and desorption, hydrogen-induced amorphization (HIA) in C15 Laves phases-GdM2 (M = Fe, Co, Ni) and crystallization of the resultant amorphous alloys a-GdM2Hx have been measured by differential scanning calorimetry (DSC). Furthermore, structures of a-GdM2Hx have been investigated by X-ray diffractometry (XRD) to correlate their structures with the stabilities of the original compounds. Both a-GdFe2H3.0 and a-GdCo2H3.4 prepared from the less stable compounds show the strong tendency for the same kinds of metal atoms to cluster and crystallize to GdH2 and Fe(Co). Correspondingly, the sum of DELTAH for all reactions become equal to that for the formation of GdH2. On the contrary, a-GdNi2H3.5 Prepared from the stable compound shows a rather homogeneous structure and crystallizes to GdH2 and GdNi5. As a result, the sum of DELTAH shows a large negative value in comparison with that for the formation of GdH2.