Simultaneous electrical and X-ray diffraction studies on neodymium metal to 152 GPa

Using designer diamond anvils and angle dispersive X-ray diffraction technique at a synchrotron source, we have performed simultaneous electrical and structural studies on neodymium metal to 152 GPa in a diamond anvil cell. Four-probe electrical resistance measurement shows a 38% decrease in the electrical resistivity, associated with the delocalization of the 4f-shell electrons, starting at 100 GPa up to a final pressure of 152 GPa. The continuous decrease in electrical resistivity is consistent with the observation of a gradual phase transition to alpha-U structure in this pressure range. The (1 1 1) diffraction peak of alpha-U structure first appears at 100 GPa and increases in intensity with increasing pressure to 152 GPa. This increase in intensity is attributed to an increasing volume fraction of alpha-U phase and an increase in structural gamma-parameter from 0.07 at 118 GPa to 0.095 at 152 GPa. In contrast to the abrupt pressure-induced f-electron transition seen in cerium and praseodymium, the continuous evolution of alpha-U structure and electrical resistivity in neodymium confirms the gradual nature of 4f delocalization process in this element.