Studies of pressure-induced disproportionation of rare-earth metal dihydrides by X-ray diffraction and infrared reflection spectroscopy

Machida, Akihiko; Sakurai, Yoko; Aoki, Katsutoshi

We have investigated the structural and electronic properties of rare-earth metal di-hydrides under high pressure. Rare-earth metal di-hydrides exhibit the fcc metal lattice, which contains hydrogen atoms in only tetrahedral interstitial sites. It is expected that the hydrogen atoms transfer to another interstitial site, such as an unoccupied octahedral site, by compression of metal lattice. We found the pressure-induced phase separation of yttrium di-hydride and lanthanum di-hydride. These results suggest that the disproportionation reaction into solid-solution and tri-hydride phases occurred under high pressure. In order to demonstrate the disproportionation reaction, we have performed infrared reflection spectroscopy for lanthanum di-hydride under high pressure and have found the formation of an insulating phase.