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

Structural changes in C15 Laves phases CeFe2 and TbFe2 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 CeFe2 always gives rise to HIA and no crystalline (c-) CeFe2Hx hydride is formed. As the temperature increases, CeH2 precipitates in amorphous (a-) CeFe2Hx and the remaining amorphous phase decomposes into CeH2 and α-Fe. On the contrary, hydrogen absorption in TbFe2 always leads to formation of c-TbFe2Hx hydride at near the room temperature. As the temperature increases, c-TbFe2Hx transforms to a-TbFe2Hx hydride, becomes a-Tb1−yFe2Hx+TbyH2 or decomposes directly into TbH2+α-Fe depending on the hydrogen pressure. As the temperature increases, TbH2 precipitate in a-TbFe2Hx hydride and the remaining amorphous phases decompose into TbH2+α-Fe. The difference in the formation process of hydrogen-induced amorphous alloys between these compounds is discussed.