Pressure dependence of hydrogen-induced amorphization in C14 Laves phase NdMn_2

摘要

Structural changes in C14 Laves phase NdMn_2 in a hydrogen atmosphere of 0.1-5.0MPa were investigated using a pressure differential scanning calorimeter (PDSC), a powder X-ray diffractometer (XRD), a conventional differential scanning calorimeter (Ar-DSC), a transmission electron microscope (TEM) and a hydrogen analyzer. Three exothermic peaks resulting from (1) hydrogen absorption in the crystalline state, (2) hydrogen-induced amorphization (HIA) and the precipitation of BiF3-type NdH_3 which occur simultaneously, and (3) the decomposition of the remaining amorphous phase into alpha-Mn and NdH_3 were observed with increasing temperature between 0.1 and 1.0 MPa H_2. HIA and the precipitation of NdH_3 occurred separately above 2.0 MPa H_2. The peak temperature for HIA of C14 Laves phase NdMn_2 and its pressure dependence is higher and smaller than those of C15 Laves phases RFe_2. HIA of NdMn_2 occurred for every hydrogen pressure, although the single phase amorphous hydride is not formed below 1.0 MPa H_2.