Frontier of High Pressure Research on Metal Hydrides

Abstract

The highly compressed state of metal hydride has been investigated to explore structural and electronic transitions characteristic to hydride. The hydrogen atoms play the lead in the transitions, showing displacement in or transfer between the interstitial sites of a metal lattice. One example is the band gap closing observed for a long period lattice of yttrium tri-hydride, YH₃, appearing at pressures above 12 GPa. Another example is photochromic event observed again for yttrium hydride, YH_x. The former is likely accompanied by the in-site displacement of hydrogen atoms and the latter by the site-to-site transfer.