Crystal structures of YH3 under high pressure

The high-pressure crystal structures of Y H3 have been extensively explored by using a genetic algorithm. Two layer-like metallic phases for Y H3 were revealed to be stable beyond the stability field of the experimental cubic phase: a hexagonal P63/mmcP63/mmc phase (197–214 GPa) and an orthorhombic Cmcm   phase (>214 GPa). Each layer in both structures is composed of similar Y zigzag chains connected by H atoms. The mechanism of the structure change from the P63/mmcP63/mmc phase to the Cmcm   phase was revealed. The P63/mmc–CmcmP63/mmc–Cmcm transition is identified as a reconstructive phase transition, which is accompanied by stacking of H atoms within layers without a major modification of the zigzag arranged Y atoms. The highly compressed Y sublattice along the cc-axis is responsible for this H reconstruction. In addition, the coordination number of the Y atoms decreases from ten to nine at the P63/mmc–CmcmP63/mmc–Cmcm transition, caused by the H reconstruction.

Research highlights
► Two new structures (P63/mmcP63/mmc and CmcmCmcm) were predicted for YH3 at high pressure.
► The mechanism of the P63/mmc–CmcmP63/mmc–Cmcm transition is revealed.
► The coordination number of the Y atoms decreases from ten to nine at the P63/mmc–CmcmP63/mmc–Cmcm transition.
► The P63/mmcP63/mmc and Cmcm structures of Y H3 are possible high-temperature superconductors.