High pressure structural phase transitions in Dysprosium to 202 GPa

High pressure structural phase transitions in heavy lanthanide metal Dysprosium (Dy) have been studied to 202 GPa (Volume Compression V/V0=0.36) in a diamond anvil cell employing copper as an internal x-ray pressure standard. The previously assigned monoclinic (C2/m) phase above 72 GPa has been reexamined and assigned to an orthorhombic phase with sixteen atoms per cell (oF16) based on structural refinements. The equation of state is presented to 202 GPa and indicates a volume change of 2.3% during the structural phase transition from distorted face-centered cubic (hR24) phase to oF16 phase at 72 GPa. The oF16 phase can be regarded as a pseudo-orthorhombic eight-layered structure with (b/c) ratio decreasing from an ideal value of 3 with increasing pressure to 202 GPa. The ultrahigh pressure structural phases of Dy are compared with other members of the lanthanide series.