Pressure dependence of hydrogen-induced amorphization in C14 Laves phase NdMn2

Structural changes in C14 Laves phase NdMn2 in a hydrogen atmosphere of 0.1-5.0 MPa 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 NdH3 which occur simultaneously, and (3) the decomposition of the remaining amorphous phase into alpha-Mn and NdH3 were observed with increasing temperature between 0.1 and 1.0 MPa H-2. HIA and the precipitation of NdH3 occurred separately above 2.0 MPa H-2. The peak temperature for HIA of C14 Laves phase NdMn2 and its pressure dependence is higher and smaller than those of C15 Laves phases RFe2. HIA of NdMn2 occurred for every hydrogen pressure, although the single phase amorphous hydride is not formed below 1.0 MPa H-2 (c) 2005 Elsevier B.V. All rights reserved.