Pressure-stabilized superconductive yttrium hydrides

The search for high-temperature superconductors has been focused on compounds containing a large fraction of hydrogen, such as SiH(4)(H(2))(2), CaH(6) and KH(6). 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 (YH(4) andYH(6)), which are stable above 110 GPa. Three types of hydrogen species with increased H contents were found, monatomic H in YH(3), monatomic H+molecular “H(2)” in YH(4) and hexagonal “H(6)” unit in YH(6). Interestingly, H atoms in YH(6) form sodalite-like cage sublattice with centered Y atom. Electron-phonon calculations revealed the superconductive potential of YH(4) and YH(6) 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 YH(3).