Stability of the high-pressure monoclinic phases in Ce and Pr metals: Comparative diffraction study and phenomenological theory
Résumé
Pressure-induced structural phase transformations in rare-earth metals Ce and Pr were studied at different temperatures with an externally heated diamond anvil cell by angle dispersive x-ray diffraction using a synchrotron source. Evidence for the presence of the monoclinic C2∕m (Z=8) phase, Pr-VII , in the pressure range 10–25 GPa has been observed. Theoretical models are proposed and the corresponding phase diagrams are worked out. They are compared to the experimental phase diagrams of cerium and praseodymium. The theory explains consistently the contradictory data on the stability of monoclinic and orthorhombic phases of Ce.