No abstract

No abstract

The intermediate valence of formally tetravalent compounds has been detected by L3 x-rayabsorption near-edge structure (XANES) in CeO& and in PrO& but not in UO2, which have the same CaFz structure and large f and ligand mixing. The intermediate valence has been found both in Ce02 and in Ce(SO4)2. 4H20, which have similar local structure but different crystal structure. We show that L3 XANES final states are a direct probe of configuration interaction between 4f" and 4f" +'L configurations in the ground state and that the weight of the 4f" +'L in the ground state can be deduced. The many-body final states arise from the characteristic properties of these materials: (i) the presence of localized 4f level above the oxygen 2p band separated by a gap 6e with relevant correlation energy Uff (Uff )5s) and (ii) mixing of 4f localized states with ligand valence orbitals such that the hybridization energy V is of the same order of magnitude as the energy separation b, E between the many-body configuration 4f" and 4f" +'L (V) bE). These insulating materials, which cannot be classified as standard mixed-valence systems, are called here interatomic intermediate-valencesystems.

No abstract

No abstract