Hydrogenation-induced microstructure changes of pseudo-binary (Pr Mg1−)Ni2 Laves compounds

Abstract Using transmission electron microscopy (TEM), we systematically investigate hydrogenation-induced microstructural changes of pseudo-binary (Pr x Mg 1− x )Ni 2 Laves compounds varying x from 0.3 to 1.0, which lead to the averaged constituent atomic-size ratio R A / R B ranging 1.34–1.47 of the supposed AB 2 compound. It is empirically known for the AB 2 Laves compounds that hydrogen-induced-amorphization (HIA) takes place when the R A / R B exceeds 1.37. We find that, based on careful analyses of electron diffraction patterns and TEM images, the hydrogenation-processed microstructures of the (Pr x Mg 1− x )Ni 2 compounds exceeding the critical ratio are not pure amorphous but composed of Ni nano-crystals embedded in an amorphous matrix of hydride PrH 2 . This provides a direct evidence of hydrogenation-induced micro-phase separation (HIMPS), and accordingly it is suggested that HIA believed so far should be attributed to HIMPS phenomenon.