AbstractThe search for high-temperature superconductors has been focused on compounds containing a large fraction of hydrogen, such as SiH₄(H₂)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 andYH₆), which are stable above 110 GPa. Three types of hydrogen species with increased H contents were found, monatomic H in YH₃, monatomic H+molecular “H₂” in YH₄ and hexagonal “H₆” 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.