Lawrence Berkeley National Laboratory
Local Symmetry Effects in Actinide 4f X-ray Absorption in Oxides.
- Author(s): Butorin, Sergei M
- Modin, Anders
- Vegelius, Johan R
- Suzuki, Michi-To
- Oppeneer, Peter M
- Andersson, David A
- Shuh, David K
- et al.
Published Web Locationhttps://doi.org/10.1021/acs.analchem.5b04380
A systematic X-ray absorption study at actinide N6,7 (4f → 6d transitions) edges was performed for light-actinide oxides including data obtained for the first time for NpO2, PuO2, and UO3. The measurements were supported by ab initio calculations based on local-density-approximation with added 5f-5f Coulomb interaction (LDA+U). Improved energy resolution compared to common experiments at actinide L(2,3) (2p → 6d transitions) edges allowed us to resolve the major structures of the unoccupied 6d density of states (DOS) and estimate the crystal-field splittings in the 6d shell directly from the spectra of light-actinide dioxides. The measurements demonstrated an enhanced sensitivity of the N(6,7) spectral shape to changes in the compound crystal structure. For nonstoichiometric NpO(2-x), the filling of the entire band gap with Np 6d states was observed thus supporting a phase coexistence of Np metal and stoichiometric NpO2 which is in agreement with the tentative Np-O phase diagram.