Pressure Dependence of Hydrogen-Induced Transformations in C15 Laves Phase DyCo₂

Abstract

Structural changes in C15 Laves phase DyCo₂ heated in a hydrogen atmosphere between 0.1 and 5.0 MPa were investigated using a pressure differential scanning calorimeter (PDSC) and were compared with those of DyFe₂. Four exothermic reactions resulting from 1) hydrogen absorption forming crystalline and amorphous hydrides, 2) hydrogen-induced amorphization (HIA), 3) the precipitation of BiF₃-type DyH₃ in the amorphous hydride and 4) the decomposition of the remaining amorphous hydride into DyH₃ + β-Co were observed with increasing temperature. HIA in DyCo₂ occurred for every hydrogen pressure in contrast to DyFe₂, because the pressure dependence of it is small. The mechanism of the phase transformations for DyCo₂ in a hydrogen atmosphere was discussed on the basis of the experimental results such as the pressure dependence of T_p and T_p/T_m (the peak temperature/the melting point of DyCo₂), the enthalpy change ΔH, the activation energy E_A and so on.