Hydrogen pressure dependence of structural changes in C15 Laves phase DyMn ₂ studied by pressure differential scanning calorimetry

C15 Laves phase DyMn ₂ was thermally analyzed using a pressure differential scanning calorimeter (PDSC) in a hydrogen atmosphere between 0.1 and 5.0 MPa and its structural changes were investigated with a powder X-ray diffraction (XRD), a conventional differential scanning calorimeter in an argon atmosphere (Ar-DSC), a transmission electron microscope (TEM) and a hydrogen analyzer. Three exothermic peaks of (1) hydrogen absorption forming a crystalline (c-) and an amorphous (a-) hydride DyMn ₂H _x; (2) the simultaneous occurrence of hydrogen-induced amorphization (HIA) and the precipitation of DyH ₃ and (3) the decomposition of the amorphous hydride into DyH ₃ + α-Mn were observed independent of the hydrogen pressure. The peak temperature T _p for all reactions showed a negative pressure dependence, and no single-phase c- and a-DyMn ₂H _x were obtained under the present experimental conditions.