A New Allotropic form of Cerium Due to its Transition Under Pressure to the Tetravalent State

Abstract

An x-ray structural analysis on cerium under pressure was made in order to investigate its valence behavior in the metallic state. A new form, ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{-}\mathrm{Ce}$, always fcc but strongly collapsed, was found to exist at pressures higher than 50 kbar. It was deduced that Ce is tetravalent in the ${\ensuremath{\alpha}}^{\ensuremath{'}}$ form. The atomic radius of ${\mathrm{Ce}}^{\mathrm{IV}}$ was calculated, and the probable values of the valency in $\ensuremath{\gamma}\ensuremath{-}\mathrm{Ce}$ and $\ensuremath{\alpha}\ensuremath{-}\mathrm{Ce}$ are also estimated.