DFT study on the electronic structure and chemical state of Americium in an (Am,U) mixed oxide

• The electronic states of Am oxides, U oxides, and CaF2-type (Am,U) mixed oxide are investigated.
• The valence of Am in the (Am,U) mixed oxide was close to that of Am2O3.
• The valence of U in the mixed oxide was pentavalent.
• The electronic states of these oxides reflected their oxygen potential.
• Charge transfer from Am in AmO2 to U in UO2 in the solid solution process of the mixed oxide.

We investigated the electronic state of an (Am,U) mixed oxide with the fluorite structure using the all-electron full potential linear augmented plane wave method and compared it with those of Am2O3, AmO2, UO2, and La0.5U0.5O2. The valence of Am in the mixed oxide was close to that of Am2O3 and the valence of U in the mixed oxide was pentavalent. The electronic structure of AmO2 was different from that of Am2O3, particularly just above the Fermi level. In addition, the electronic states of Am and U in the mixed oxide were similar to those of trivalent Am and pentavalent U oxides. These electronic states reflected the high oxygen potential of AmO2 and the heightened oxygen potential resulting from the addition of Am to UO2 and also suggested the occurrence of charge transfer from Am to U in the solid solution process.