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

The structural changes of CeRU2 during hydrogen absorption or desorpti on are examined by X-ray diffraction, differential scanning calorimetr y and transmission electron microscopy. CeRU2 decomposes into the micr ocrystalline phases CeH2 and alpha-Ru upon hydrogenation at 400-degree s-C. The crystalline hydride phase is amorphized by partial desorption of hydrogen even at room temperature. To examine the amorphization me chanism, some of the Ce atoms are replaced by Gd atoms within the stab ility range of the C15 Laves structure. As the fraction of Gd increase s, the degree of amorphization becomes lower. It is proposed that the amorphization of (Ce, Gd)Ru2 hydride is closely related to the presenc e of Ce and H atoms. The large volume change during hydrogen desorptio n may lead to elastic instability of the compound and the remaining H atoms stabilize the amorphous structure.