AMORPHIZATION OF THE CRYSTALLINE CERU2 HYDRIDE AND THE EFFECTS OF GD SUBSTITUTION ON THE AMORPHIZATION BEHAVIOR

Abstract

The structural changes of CeRU2 during hydrogen absorption or desorption are examined by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. CeRU2 decomposes into the microcrystalline phases CeH2 and alpha-Ru upon hydrogenation at 400-degrees-C. The crystalline hydride phase is amorphized by partial desorption of hydrogen even at room temperature. To examine the amorphization mechanism, some of the Ce atoms are replaced by Gd atoms within the stability range of the C15 Laves structure. As the fraction of Gd increases, the degree of amorphization becomes lower. It is proposed that the amorphization of (Ce, Gd)Ru2 hydride is closely related to the presence of Ce and H atoms. The large volume change during hydrogen desorption may lead to elastic instability of the compound and the remaining H atoms stabilize the amorphous structure.