Dresden 2026 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 88: Catalysis and surface reactions III

O 88.7: Vortrag

Donnerstag, 12. März 2026, 16:30–16:45, TRE/MATH

Beyond U-Ce charge transfer: stabilization of Ce³⁺ states in epitaxial Ce_1−xU_xO₂ films grown on Ru(0001) — •Carlos Morales¹, Rudi Tschammer¹, Thomas Gouder², Hicham Idriss³, and Jan Ingo Flege¹ — ¹Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology, Cottbus, Germany — ²European Commission, Joint Research Centre (JRC), Karlsruhe, Germany — ³Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Cerium oxide (CeO₂) stands out among reducible metal oxides for its stability and activity. Yet, promoting Ce³⁺ active states requires high energy. The conversion of Ce⁴⁺ to Ce³⁺ at lower temperatures for the thermochemical splitting of H₂O or CO₂ can be enhanced by doping ceria with other elements. Particularly, ceria mixing with uranium has been proven successful: substituting a fraction of Ce⁴⁺ by U⁴⁺ results in a charge transfer that promotes the formation of Ce³⁺ and U⁵⁺ states. We have explored the redox properties of 8 nm thick epitaxial (111)-oriented Ce_1−xU_xO₂ on Ru(0001). In line with previous studies focused on polycrystalline powders, the as-grown films exhibit a high Ce⁴⁺ to Ce³⁺ conversion, with a maximum reduction corresponding to approximately 20 % of U content. However, the concentration of Ce³⁺ states and oxygen is higher than predicted by density function theory (DFT) calculations for various U contents and spatial ordering. The observed behaviour could be likely related to the lattice distortion caused by the significant difference in the ionic radii of Ce³⁺ and U⁵⁺. This effect has not been considered before in Ce_1−xU_xO₂ mixed oxides.

Keywords: CeO2; Uranium; Epitaxy; XPS; DFT