Hydrogen-induced transformations in C15 Laves phases CeFe2 and TbFe2 studied by pressure calorimetry up to 5 MPa

Structural changes in C15 Laves phases CeFe 2 and TbFe 2 during thermal analysis in a hydrogen atmosphere (0.1∼5.0 MPa) were examined using pressure differential scanning calorimetry (PDSC) in order to compare conditions of hydrogen-induced amorphization (HIA). In the pressure range investigated hydrogen absorption in CeFe 2 always gives rise to HIA and no crystalline ( c -) CeFe 2 H x hydride is formed. As the temperature increases, CeH 2 precipitates in amorphous ( a -) CeFe 2 H x and the remaining amorphous phase decomposes into CeH 2 and α-Fe. On the contrary, hydrogen absorption in TbFe 2 always leads to formation of c -TbFe 2 H x hydride at near the room temperature. As the temperature increases, c -TbFe 2 H x transforms to a -TbFe 2 H x hydride, becomes a -Tb 1− y Fe 2 H x +Tb y H 2 or decomposes directly into TbH 2 +α-Fe depending on the hydrogen pressure. As the temperature increases, TbH 2 precipitate in a -TbFe 2 H x hydride and the remaining amorphous phases decompose into TbH 2 +α-Fe. The difference in the formation process of hydrogen-induced amorphous alloys between these compounds is discussed.