Pressure-induced structural transition in rare-earth metal hydrides

Machida, Akihiko; Watanuki, Tetsu; Omura, Ayako*; Aoki, Katsutoshi; Takemura, Kenichi*

Pressure induced structural transitions of rare-earth metal hydrides have been investigated under hydrostatic pressure at room temperature. Tri-hydride, YH, exhibits a hexagonal metal lattice containing three hydrogen atoms per metal atom in the interstitial spaces: two hydrogen atoms at the tetrahedral sites and one hydrogen atom near the Y metal plane in the octahedral sites. We observed the pressure-induced structural transformation from the hexagonal metal lattice into a face-centered cubic (fcc) one through an intermediate state, which appears in the wide pressure span of 12-22 GPa. The obtained X-ray diffraction patterns in the intermediate state are represented by long-period rhombohedral structures. These long-period structures gradually transform toward the fcc metal lattice with successively increasing in the fcc-type component in a unit cell upon compression.