Long-period stacking structures in yttrium trihydride at high pressure

The pressure-induced structural transition of YH3 has been investigated by x-ray diffraction experiments under hydrostatic pressure at room temperature. The diffraction patterns of the intermediate state between the hexagonal and cubic phases are interpreted in terms of long-period polytypes with the periodic arrangements of hexagonal-type and fcc-type stacking layers of the Y metals. The hydrogen-hydrogen repulsive interactions and hydrogen-metal bonding likely play a dominant role in the gradual hexagonal-fcc lattice conversion via the long-period polytypic structures.