Diffraction and coherent diffuse quasielastic scattering of neutrons have been used to investigate Frenkel disorder of the oxygen sublattice in single crystals of stoichiometric U${\mathrm{O}}_2$. Measurements were made up to 2900 K using a special high-temperature furnace. The results provide the first direct evidence for the occurrence of Frenkel disorder in U${\mathrm{O}}_2$ and enable estimates of the defect concentration and activation energy to be made.

• Received 13 December 1983

DOI:https://doi.org/10.1103/PhysRevLett.52.1238