Ion scattering and Auger-electron spectroscopies show that there is a large segregation of uranium at the surface of U${\mathrm{Fe}}_2$. Adsorbed oxygen reacts only with this uranium and forms a stable oxide layer at the surface, which prevents further oxygen diffusing into the solid. As a result of this process, the iron remains in metallic form even after prolonged oxygen exposures.

• Received 22 March 1985

DOI:https://doi.org/10.1103/PhysRevB.32.2667