| AVS 60th International Symposium and Exhibition | |
| Actinides and Rare Earths Focus Topic | Tuesday Sessions |
| Session AC+AS+EN-TuA |
| Session: | Actinides and Rare Earths: The Nuclear Fuel Cycle and Critical Materials |
| Presenter: | S. Minasian, Lawrence Berkeley National Lab (LBNL) |
| Authors: | S. Minasian, Lawrence Berkeley National Lab (LBNL) J. Keith, Los Alamos National Lab (LANL) E. Batista, Los Alamos National Lab (LANL) K. Boland, Los Alamos National Lab (LANL) J. Bradley, Lawrence Livermore National Laboratory (LLNL) S. Daly, George Washington Univ. S. Kozimor, LANL W. Lukens, LBNL R.L. Martin, LANL D. Nordlund, SLAC National Accelerator Lab G. Seidler, Univ. of Washington D. Shuh, LBNL D. Sokaras, SLAC National Accelerator Lab T. Tyliszczak, LBNL G. Wagner, LANL T.-C. Weng, SLAC National Accelerator Lab P. Yang, Pacific Northwest National Lab |
| Correspondent: | Click to Email |
Developing a clear understanding of how metal oxide electronic structure changes for a range compounds and materials will greatly benefit a variety of existing and emerging energy technologies. Many of the technologically desirable chemical, magnetic, electronic, and thermal properties of metal oxides are derived from strongly covalent metal–oxygen multiple bonds (metal oxos). Among approaches explored previously, ligand K-edge X-ray absorption spectroscopy (XAS) has emerged as an effective method for quantitatively probing electronic structure and orbital mixing. The presence of covalent mixing is observed as a pre-edge feature in the ligand K-edge XAS, which only has transition intensity if the final state metal orbital contains a component of ligand p orbital character. Recent advances have shown that insights regarding the nature of orbital mixing in metal oxides can be obtained at the K-edge for oxygen through a combination of XAS with a scanning transmission X-ray microscope (STXM), non-resonant inelastic X-ray scattering (NIXS), and hybrid density functional theory calculations (DFT). The spectroscopic work in this study was performed at the ALS Molecular Environmental Sciences beamline 11.0.2 (STXM), beamline 6.2 at SSRL (NIXS), and the LERIX facility at the APS (NIXS).
Herein, a new effort is discussed that employs these techniques to understand bonding interactions in d- and f-block oxides. Oxygen K-edge XAS measurements and DFT studies began with a series of six tetrahedral oxyanions, MO42- and MO41- (M = Cr, Mo W and Mn, Tc, Re). Despite the similarities of the isoelectronic d0 MO42- and MO41- anions, unexpected differences in metal oxo orbital mixing were observed for adjacent metals in the periodic table. The lanthanide dioxides and sesquioxides, LnO2 and Ln2O3 (Ln = Ce, Pr, Tb), were chosen for subsequent work because their electronic structures are well-established from hard X-ray spectroscopies. Features in the O K-edge XAS follow anticipated trends based on 4f and 5d orbital energies and occupancies. Taken together with L3-edge intensities determined previously, a detailed picture of the electronic structure in lanthanide oxides emerges. Overall, the research shows that orbital composition is influenced by a complex interplay between periodic changes in both orbital energy and radial extension.
This work was funded by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under contracts DE-AC02-05CH11231 at LBNL and DE-AC52-06NA25396 at LANL. Operation of the ALS, SSRL, and the APS is supported by the U.S. Department of Energy, Office of Science.