Phase transformations and equation of state of praseodymium metal to 103 GPa

Abstract

Pressure-induced structural phase transformations in a trivalent rare-earth metal praseodymium (Pr) were studied at room temperature in a diamond anvil cell to 103 GPa by energy dispersive x-ray diffraction using a synchrotron source. Our x-ray diffraction studies document the following crystal structure sequence: $\mathrm{dhc}\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{fc}\stackrel{\ensuremath{\rightarrow}}{c}\mathrm{distorted}\mathrm{}\mathrm{fcc}(hR24\mathrm{type})\ensuremath{\rightarrow}\mathrm{monoclinic}(C2/m)\ensuremath{\rightarrow}\ensuremath{\alpha}\ensuremath{-}$uranium with increasing pressure. We measure a 16.7% volume collapse at the transition to the \ensuremath{\alpha}-uranium phase at 20 GPa. The high-pressure \ensuremath{\alpha}-uranium phase in Pr was found to be stable to the highest pressure of 103 GPa, which corresponds to a volume compression ${V/V}_{0}=0.407.$