High-pressure structures of yttrium hydrides.

In this work, the crystal structures of YH and YH at high pressure (100-250 GPa) have been explored using a genetic algorithm combined with first-principles calculations. New structures of YH with space group symmetries of P21/m and I4/mmm were predicted. The electronic structures and the phonon dispersion properties of various YH and YH structures at different temperatures and pressures were investigated. Among YH phases, the P21/m structure of YH was found to have a relatively high superconducting transformation temperature T of 19 K at 120 GPa, which is reduced to 9 K at 200 GPa. Other YH structures have much lower T s. Compared with YH, the T of the YH compound is much higher, i.e. 94 K at 120 GPa and 55 K at 200 GPa.