Existing Phase Diagrams Research Articles

The electrical properties of uranium oxides

The electrical conductivity and thermoelectric power of uranium oxides in the UO 2U 3O 7 range have been studied at temperatures between 27 and 400°C after annealing at various elevated temperatures. The following compounds were identified: UO 2+ x , a metal-deficit semiconductor; U 4O 9− y , a metal-excess semiconductor; and U 3O 7− z , a metal-excess semiconductor. The presence of all major phases was confirmed by X-ray powder techniques. An energy of about 0·4 eV is required to free a positive carrier from the interstitial oxygen in UO 2+ x . In U 4O 9 or U 3O 7 the energy required to free an electron from the hexavalent uranium varies from 0·4 eV at high carrier concentrations to 0·9 eV at the lower concentrations. The electrical properties of the oxides are interpreted in terms of the phase relationships of the UO 2U 3O 7 system and certain modifications of existing phase diagrams are suggested.