Process and mechanism of hydrogen-induced amorphization in C15 Laves phases RFe 2

Abstract

The pressure dependence of structural changes in C15 Laves phase DyFe 2 was investigated using a pressure differential scanning calorimeter (PDSC) at 0.1–5.0 MPa H 2 and compared with that of ErFe 2 and CeFe 2. By thermal analysis of DyFe 2, four exothermic peaks of hydrogen absorption, hydrogen-induced amorphization (HIA), the precipitation of BiF 3-type DyH 3 and the decomposition of the amorphous hydride were observed above 0.5 MPa H 2, although tri-hydride DyH 3 takes usually the HoH 3-type structure. HIA overlapped with the precipitation of DyH 3 at 0.2 MPa H 2, but c-DyFe 2H x decomposed directly into α -Fe and DyH 3at 0.1 MPa H 2. Hydrogen absorption, HIA, and the decomposition of a-DyFe 2H x showed a negative pressure dependence, but the precipitation of DyH 3 showed a positive one. As a result of such dependence, HIA does not occur at lower hydrogen pressure. The structural changes of ErFe 2were similar to that of DyFe 2. On the other hand, hydrogen absorption and HIA occurred simultaneously for every hydrogen pressure in CeFe 2. The mechanism of HIA in the C15 Laves phases RFe 2 was discussed on the basis of the experimental results.