A neutron powder diffraction study of U1–yCeyO2–x

Abstract

Neutron powder diffraction has been used to study the two-phase behaviour in U_1–yCe_yO_2–x. At room temperatures two-phase behaviour is observed for samples having y > 0.25 and x > 0.03. The two phases appear to have compositions corresponding to almost stoichiometric (MO₂) and reduced (MO_2–x) fluorite structures. For samples close to the theoretical limit of the reduction (O/M = 2 –y/2), a single phase of type MO_2–x forms. Studies made at temperatures up to 250 °C show a redistribution of the oxygen atoms, implying that as the temperature increases, a single-phase mixed oxide will result for all values of y.