抄録
In order to investigate the processes of amorphization and phase separation in the YNi2-H system, we studied the feature of structural changes in the YNi2-H system by X-ray diffraction method and thermal analysis as a function of hydriding temperature and time under a hydrogen pressure of 1 MPa. From the X-ray diffraction and differential thermal analysis, it was demonstrated that the amorphization reaction for hydriding at 473 K is much delayed in comparison with those at 573 and 273 K. This temperature dependence of the formation rate of the amorphous phase can be qualitatively explained by considering two promoting factors for Ni-diffusion, the lattice expansion by hydrogen absorption and thermal activation. We could also clarify that yttrium-rich tetrahedral sites (3Y+1Ni) increase with increasing hydriding temperature and time by analyzing the differential thermogravimetric data. In particular, when the hydriding temperature is high enough, the yttrium-rich sites in the amorphous phase drastically increase. This suggests that the growth of yttrium-rich and nickel-rich clusters occurs in the amorphous structure, which may be recognized as a pre-phenomenon of the phase separation into YHx and YNi3+δ phases.
