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

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, α^'-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 α^' form. The atomic radius of CeIV was calculated, and the probable values of the valency in γ-Ce and α-Ce are also estimated.