Structural transformations of dysprosium up to 337 GPa

The structures and equations of states of dysprosium have been studied up to 337 GPa without a pressure transmitting medium using synchrotron x-ray diffraction. Beyond the previously reported transition sequences, namely hP2 \ensuremath{\rightarrow} hR9 \ensuremath{\rightarrow} hP4 \ensuremath{\rightarrow} hR24 \ensuremath{\rightarrow} oF16, we herein disclose an isosymmetric structural transition that occurs above 195.5 GPa, wherein the structure transforms from orthorhombic face-centered oF16 to oF8. The oF8 phase comprises eight atoms per unit cell and belongs to the space group Fddd, being isostructural with lanthanides Nd-VI, Sm-VI, and actinides Am-III, Cf-III, and Cm-IV. During the phase transition, the reduction in lattice volume occurs continuously and is concomitant with the expansion along the $b$ axis, manifesting negative linear compressibility and an increasing degree of anisotropy. Our finding further corroborates the intimate structural correlation between lanthanides and actinides.