Under ambient conditions, praseodymium metal possesses a localized $4f^2$-electron configuration. Near 20 GPa, the lattice volume collapses by $~$10% into the $\alpha$-uranium crystal structure, and the electrical resistivity drops dramatically. This behavior is similar to that observed in cerium metal and has been taken as evidence for $4f$ delocalization, although the precise nature of such volume collapse transitions in rare-earth metals is still a matter of debate. Since cerium metal develops superconductivity in the collapsed phase, we undertook a search for superconductivity in praseodymium metal at high pressure. Using designer diamond anvils, we measured the electrical resistivity of high purity praseodymium metal to pressures above 1 Mbar and millikelvin temperatures. No evidence for superconductivity was found in any of the measurements. The lack of superconductivity may derive from magnetic pair-breaking effects related to incomplete screening/delocalization of the $4f$-electron state.

• Received 8 March 2011

DOI:https://doi.org/10.1103/PhysRevB.84.033101