| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Thursday Sessions |
| Session AC+AS+SA-ThM |
| Session: | Chemistry and Physics of the Actinides and Rare Earths |
| Presenter: | Stefan Minasian, Lawrence Berkeley National Laboratory (LBNL) |
| Authors: | S.G. Minasian, Lawrence Berkeley National Laboratory (LBNL) A.B. Altman, University of California at Berkeley J. Arnold, University of California at Berkeley E.D. Bauer, Los Alamos National Laboratory C.H. Booth, Lawrence Berkeley National Laboratory (LBNL) J.I. Pacold, Lawrence Berkeley National Laboratory (LBNL) C.D. Pemmaraju, Lawrence Berkeley National Laboratory (LBNL) D.G. Prendergast, Lawrence Berkeley National Laboratory (LBNL) D.K. Shuh, Lawrence Berkeley National Laboratory (LBNL) T. Tyliszczak, Lawrence Berkeley National Laboratory (LBNL) |
| Correspondent: | Click to Email |
For most scientific and technical applications, aluminum is well-regarded as a trivalent, electropositive and Lewis-acidic metal. However, this textbook model fails to adequately explain the unusual chemical and physical properties of many f-element molecules, materials, and alloys incorporating aluminum and other group 13 elements. In order to develop a more nuanced model of aluminum electronic structure, we have turned to metal K-edge X-ray Absorption Spectroscopy (XAS), which is an established technique for evaluating electronic structure in bioinorganic and inorganic compounds. Pre-edge peaks in K-edge XAS correspond to bound state transitions between core and unoccupied orbitals. Therefore, by comparing pre-edge features to established references, information can be gathered on the electronic structure of a system and the orbitals involved in bonding. However, there is very little precedent for the measurement and interpretation of aluminum K-edge XAS for molecules and materials.
This presentation will describe our recent efforts to develop Al K-edge XAS as a probe of chemical bonding and electronic structure in Al molecules and materials with lanthanide and actinide metals. Work began by examining a series of molecular aluminum compounds and by systematically varying supporting ligands and oxidation states. Features in the Al K-edge spectra were fully assigned through a comprehensive polarization study and comparison with the results of XCH and DFT calculations. Results were interpreted within a molecular orbital framework, providing unique insight that could not be obtained from analysis of NMR or metrics from single-crystal X-ray diffraction. These results have laid a foundation for ongoing efforts with lanthanide and actinide aluminum alloys, MAl2 (M = Ce, Sm, Eu, Yb, Lu, U, and Pu). Comparisons between the Al K-edge spectra and earlier resonant X-ray emission spectra for the MAl2 compounds provide unique insight into how electronic structure influences the desirable physical properties of these materials. For EuAl2 and YbAl2, the increasing occupancy of the 4f orbitals enhances screening of the 5d orbitals, resulting in enhanced Al 3p and Ln 5d orbital mixing for Eu and Yb that is not observed for Ce, Sm, or Lu. For UAl2 and PuAl2, the Al K-edge XAS and theory results also provides convincing evidence of Al 3p and 6d orbital mixing. Because of the enhance radial extension of the 6d orbitals, 6d orbital involvement in bonding for PuAl2 is more likely to have an impact on the stability of the Pu–Al bonds. Current efforts are focused on evaluating f-element interactions with aluminum in other stoichiometric and non-stoichiometric alloys.