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

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: dhcp⃗fcc⃗distorted fcc(hR24type)→monoclinic(C2/m)→α-uranium with increasing pressure. We measure a 16.7% volume collapse at the transition to the α-uranium phase at 20 GPa. The high-pressure α-uranium phase in Pr was found to be stable to the highest pressure of 103 GPa, which corresponds to a volume compression V/V₀=0.407.