title: Crystal-Field and Covalency Effects in Uranates: An X-ray Spectroscopic Study.
abstract: The electronic structure of U(V) - and U(VI) -containing uranates NaUO3 and Pb3 UO6 was studied by using an advanced technique, namely X-ray absorption spectroscopy (XAS) in high-energy-resolution fluorescence-detection (HERFD) mode. Due to a significant reduction in core-hole lifetime broadening, the crystal-field splittings of the 5f shell were probed directly in HERFD-XAS spectra collected at the U 3d edge, which is not possible by using conventional XAS. In addition, the charge-transfer satellites that result from U 5f-O 2p hybridization were clearly resolved. The crystal-field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated by using the Anderson impurity model by calculating the U 3d HERFD-XAS, conventional XAS, core-to-core (U 4f-3d transitions) resonant inelastic X-ray scattering (RIXS), and U 4f X-ray photoelectron spectra. The crystal field was found to be strong in these systems and the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO3 and Pb3 UO6 , respectively, which indicates a significant covalent character for these compounds.
authors.affiliation: Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, P. O. Box 516, 751 20, Uppsala, Sweden. sergei.butorin@physics.uu.se.
authors.forename: Sergei M
authors.initials: SM
authors.lastname: Butorin
authors.affiliation: European Synchrotron Radiation Facility, CS40220, 38043, Grenoble Cedex 9, France.|Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 510119, 01314, Dresden, Germany.
authors.forename: Kristina O
authors.initials: KO
authors.lastname: Kvashnina
authors.affiliation: Department of Radiation Science and Technology, TU Delft, Mekelweg 15, 2629 JB, Delft, Netherlands.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Smith
authors.affiliation: European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, 76125, Karlsruhe, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Popa
authors.affiliation: CEA Marcoule, CEA, DEN, DTEC/SECA/LCC, 30207, Bagnols-sur-Cèze Cedex, France.
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Martin
keywords: X-ray absorption spectroscopy; computational chemistry; crystal-field studies; electronic structure; uranium