Process and mechanism of hydrogen-induced amorphization in C15 Laves phases RFe2

The pressure dependence of structural changes in C15 Laves phase DyFe2 was investigated using a pressure differential scanning calorimeter (PDSC) at 0.1-5.0 MPa H-2 and compared with that of ErFe2 and CeFe2. By thermal analysis of DyFe2, four exothermic peaks of hydrogen absorption, hydrogen-induced amorphization (HIA), the precipitation of BiF3-type DyH3 and the decomposition of the amorphous hydride were observed above 0.5 MPa H-2, although tri-hydride DyH3 takes usually the HoH3-type structure. HIA overlapped with the precipitation of DyH3 at 0.2 MPa H-2, but c-DyFe2Hx decomposed directly into alpha-Fe and DyH3 at 0.1 MPaH2. Hydrogen absorption, HIA, and the decomposition of alpha-DyFe2Hx showed a negative pressure dependence, but the precipitation of DyH3 showed a positive one. As a result of such dependence, HIA does not occur at lower hydrogen pressure. The structural changes of ErFe2 were similar to that of DyFe2. On the other hand, hydrogen absorption and HIA occurred simultaneously for every hydrogen pressure in CeFe2. The mechanism of HIA in the C15 Laves phases RFe2 was discussed on the basis of the experimental results. (c) 2005 Elsevier B.V. All rights reserved.