α-uranium phase in compressed neodymium metal

The light rare-earth metal, neodymium, has been studied up to 155 GPa in a diamond-anvil cell using energy dispersive x-ray diffraction with a synchrotron source. The pressures were calibrated using copper as an internal x-ray pressure standard. A phase transformation from a monoclinic phase (C2/m, 4 atoms/cell) to an orthorhombic alpha-U phase (Cmcm, 4 atoms/cell) was observed at 113+/-6 GPa without any observable volume collapse. The observation of alpha-U phase in Nd and, previously, in cerium and praseodymium clearly establishes this phase in light rare-earth metals. Our equation of state measurements suggest: that delocalization of the f shell in Nd occurs without any volume collapse unlike Ce and Pr.