Pressure dependence of Hydrogen-Induced Transformations in C15 Laves phase DyCo2

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 Tp and Tp/Tm (the peak temperature/the melting point of DyCo2), the enthalpy change ΔH, the activation energy EA and so on.