HYDROGEN-INDUCED TRANSFORMATION TO AN AMORPHOUS STATE IN THE LAVES PHASES CE(RU, M)2 (M EQUIVALENT-TO FE, CO, NI)

Abstract

The structural changes of the Laves phases Ce(Ru1-xMx)2, where x = 0.05-0.25 and M is the transition elements, such as Fe, Co and Ni, during hydrogen absorption are investigated through X-ray diffraction (XRD), transmission electron microscopy and differential scanning calorimetry (DSC). All the examined ternary alloys, regardless of the composition and the species of the third elements, can be amorphized by hydrogen absorption at room temperature, even though the binary CeRu2 alloy absorbs hydrogen in the crystalline hydride state. The amorphization mechanism is suggested to be identical to that of the binary CeM2 Laves phases, indicating that the elastic strain caused by hydrogen plays a key role in the amorphization. The critical strain applied on the Ce(Ru0.75Ni0.25)2 compound prior to amorphization is calculated through the DSC and XRD analysis, and it is about 1.9+/-0.5 vol.%. It is proposed that the distinct change in the hydrogenation properties of the CeRu2 system by this substitution is caused by the build-up of the lattice distortion owing to the presence of the third element, which has a smaller atomic radius.