Chemical bonding in americium oxides probed by X-ray spectroscopy

Abstract

The electronic structure and the chemical state in Am binary oxides and Am-doped UO$$_2$$ 2 were studied by means of X-ray absorption spectroscopy at shallow Am core (4d and 5d) edges. In particular, the Am 5f states were probed and the nature of their bonding to the oxygen states was analyzed. The interpretation of the experimental data was supported by the Anderson impurity model (AIM) calculations which took into account the full multiplet structure due to the interaction between 5f electrons as well as the interaction with the core hole. The sensitivity of the branching ratio of the Am $$4d_{3/2}$$ 4 d 3 / 2 and $$4d_{5/2}$$ 4 d 5 / 2 X-ray absorption lines to the chemical state of Am was shown using Am binary oxides as reference systems. The observed ratio for Am-doped UO$$_2$$ 2 suggests that at least at low Am concentrations, americium is in the Am(III) state in the UO$$_2$$ 2 lattice. To confirm the validity of the applied AIM approach, the analysis of the Am 4f X-ray photoelectron spectra of AmO$$_2$$ 2 and Am$$_2$$ 2 O$$_3$$ 3 was also performed which revealed a good agreement between experiment and calculations. As a whole, AmO$$_2$$ 2 can be classified as the charge-transfer compound with the 5f occupancy ($$n_f$$ n f ) equal to 5.73 electrons, while Am$$_2$$ 2 O$$_3$$ 3 is rather a Mott–Hubbard system with $$n_f$$ n f = 6.05.

Contemporary Assessment of Energy Degeneracy in Orbital Mixing with Tetravalent f-Block Compounds

“…However, in contrast to the LnO 2 system, AnO 2 compounds have been reported for Th–Cf, − which points to the enhanced ability of the 5f series to accommodate a tetravalent oxidation state. While XANES and XPS spectra at different absorption edges have been reported for UO 2 , the AnO 2 compounds from Np to Cf are undercharacterized, and few XAS spectra have been published. − Some of the available literature is presented in this section showing the similar metal–ligand bonding motif found in AnO 2 compared to LnO 2 and a maximum in LMCT character between Am and Cm supported by experimental determination of the energy degeneracy between An 5f and O 2p orbitals.…”

Long-term, sustainable solutions to radioactive waste management

“…6 Massachusetts Institute of Technology, Cambridge, MA, USA. 7 Investing in fundamental research and the development of new technologies for waste treatment and disposal can lead to more efficient and cost-effective methods. Our collection features several articles on fundamental science, with a particular focus on investigating the electronic structure of actinide materials, which plays a significant role in radioactive waste management.…”

“…Our collection features several articles on fundamental science, with a particular focus on investigating the electronic structure of actinide materials, which plays a significant role in radioactive waste management. Butorin and his co-authors 7 conducted research on americium oxide, an important component of the nuclear fuel cycle, using soft XAS and electronic structure calculations. Their study revealed that AmO 2 can be classified as a charge-transfer compound with a 5f.…”