Pressure dependence of hydrogen-induced amorphization in C14 Laves phase NdMn 2

Abstract

Structural changes in C14 Laves phase NdMn 2 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 BiF 3-type NdH 3 which occur simultaneously, and (3) the decomposition of the remaining amorphous phase into α -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.