Crystal structures of 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 P 6 3 / m m c 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 P 6 3 / m m c phase to the Cmcm phase was revealed. The P 6 3 / m m c – C m c m 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 c -axis is responsible for this H reconstruction. In addition, the coordination number of the Y atoms decreases from ten to nine at the P 6 3 / m m c – C m c m transition, caused by the H reconstruction.