Pressure-stabilized superconductive yttrium hydrides

The search for high-temperature superconductors has been focused on compounds containing a large fraction of hydrogen, such as SiH4(H-2)(2), CaH6 and KH6. Through a systematic investigation of yttrium hydrides at different hydrogen contents using an structure prediction method based on the particle swarm optimization algorithm, we have predicted two new yttrium hydrides (YH4 and YH6), which are stable above 110 GPa. Three types of hydrogen species with increased H contents were found, monatomic H in YH3, monatomic H+molecular H-2 in YH4 and hexagonal H-6 unit in YH6. Interestingly, H atoms in YH6 form sodalite-like cage sublattice with centered Y atom. Electron-phonon calculations revealed the superconductive potential of YH4 and YH6 with estimated transition temperatures (T-c) of 84-95 K and 251-264 K at 120 GPa, respectively. These values are higher than the predicted maximal T-c of 40 K in YH3.