Abstract
This article reports the recent studies of the pressure-induced phase separation of rare-earth metal dihydrides, which have a face-centered-cubic (fcc) metal lattice with tetrahedral interstitial sites fully occupied. Synchrotron radiation x-ray diffraction patterns of LaH2.3 show that additional Bragg reflections appeared just outside of the original ones around 11 GPa, indicating the formation of the small fcc metal lattice. The coexistence state of two fcc metal lattices thus observed is interpreted in terms of phase separation from the dihydride toward lower and higher concentration phases. The formation of insulating LaH2+δ (δ≥0.7) is confirmed by infrared spectroscopy, which shows decrease in reflection intensity. These results indicate that the interstitial hydrogen atoms transfer from T-sites and the domains of solid solution and higher concentration hydride are formed. Pressure-induced phase separation of metal hydrides would develop a new research field, that is, the dynamics of hydrogen transfer in a metal lattice.
