A differential scanning calorimetry study of hydrogen-induced amorphizatiqn in GdMn 2, PrMn 2 and NdMn 2 laves phases

Abstract

Comparative studies on hydrogen-induced amorphization in the GdMn 2, PrMn 2 and NdMn 2 Laves phases were performed using differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy measurements in order to understand hydrogen-induced amorphization phenomena. In all of the RMn 2 ( R ≡ Gd, Pr, Nd) Laves phases, two exothermic reaction peaks, which are related to crystalline hydride formation and the formation of microcrystals of RH 2 and α-Mn, are observed in the DSC trace performed in a H 2 atmosphere. Only GdMn 2 shows the phenomenon of hydrogeninduced amorphization when hydrogenated isothermally at an elevated temperature and a high hydrogen pressure. Hydrogen-induced amorphization was not observed in the PrMn 2 and NdMn 2 Laves phases. PrH 2, NdH 2 and α-Mn grow in crystalline hydride phases in the PrMn 2 and NdMn 2 phases. The activation energies for the formation of microcrystalline phases in GdMn 2, PrMn 2 and NdMn 2, determined by Kissinger's method, were found to be 21.6, 42.7 and 39.4 kcal mol −1 respectively. From the present results, the mechanism of hydrogen-induced amorphization and the atomic environments around hydrogen atoms in the amorphous state are discussed. The mechanism of amorphization would be related to the motion of manganese atoms within short range distances. The surroundings of the hydrogen atoms seem to be similar to the configurations of hydrogen atoms in GdH 2.