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

摘要

C15 Laves phase DyMn_2 was thermally analyzed using a pressure differential scanning calorimeter (PDSC) in a hydrogen atmosphere between 0.1 and 5.0MPa 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 (o) 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 + a-Mn were observed independent of the hydrogen pressure. The peak temperature Tp for all reactions showed a negative pressure dependence, and no single-phase c- and a-DyMn_2Hi- were obtained under the present experimental conditions.