Speaker
s m butorin
Description
X-ray absorption and emission spectroscopic study at O K-edges of light actinide oxides
S. M. Butorin,1 A. Modin1, Y. Yun1, M.-T. Suzuki1, J. Vegelius1, L. Werme1,
D. K. Shuh2, P. M. Oppeneer1, J. Nordgren1,
1 Depatment of Physics and Astronomy, Uppsala University, Box 516, S-751 20 Uppsala, Sweden, e-mail: sergei.butorin@fysik.uu.se
2 Lawrence Berkeley National Laboratory, Chemical Sciences Division, Mail Stop 6R2100, One Cyclotron Road, Berkeley, CA 94720, USA
Here we present soft X-ray emission and X-ray absorption spectroscopic data recorded at O K edges of UO2, NpO2 and PuO2. Interpretation of the experimental data is supported by first-principle calculations in framework of LDA+U and GGA+U formalisms (see Fig. 1). A discussion regarding the origin of different structures in the X-ray emission and X-ray absorption spectra is included. The effect of varying intra-atomic Coulomb interaction U for the f-electrons is investigated. Our data indicate that O-K X-ray absorption and X-ray emission spectroscopies can successfully be used to study correlation effects in compounds of light actinides.
For single-crystal Pu(239 isotope)O2, the measured O 1s X-ray absorption spectra show significant difference in intensity for the first two peaks between different areas/spots on the single crystal surface. From theoretical results, the first peak can be attributed to O 2p-Pu 5f hybridization, while the second peak is due to hybridization with Pu d-states. The observed difference in the O 1s X-ray absorption spectra was studied by simulating a number of defect structures of PuO2 as well as existence of Pu(V) sites. The results indicates the presence of higher oxidation states than Pu(IV) in some surface areas of the single crystal. The results also suggest that plutonium oxide with a Pu fraction in a higher oxidation state than Pu(IV) consists of inequivalent sites with Pu(IV)O2 and Pu(V)O2 rather than is being a system where the Pu oxidation state is constantly fluctuating between Pu(IV) an Pu(V).
Oral presentation.
Fig.1 Comparison of experimentally recorded (in red) and LDA+U calculated (in blue) O K X-ray emission and O 1s X-ray absorption spectra of UO2, NpO2 and PuO2.
