Effective coordination numbers from EXAFS: general approaches for lanthanide and actinide dioxides

• Published in: Journal of synchrotron radiation 2022-03, Vol.29 (2), p.288-294
• Main Authors: Romanchuk, Anna, Trigub, Alexander, Plakhova, Tatiana, Kuzenkova, Anastasiia, Svetogorov, Roman, Kvashnina, Kristina, Kalmykov, Stepan
• Format: Article
• Language: English
• Subjects: actinide; Actinide Physics and Chemistry; cerium; Cerium oxides; coordination number; Coordination numbers; extended X‐ray absorption fine structure (EXAFS); Fine structure; Metal shells; Nanoparticles; plutonium; Plutonium dioxide; Thorium oxides; Uranium dioxide
• ISSN: 1600-5775; 0909-0495; 1600-5775
• DOI: 10.1107/S160057752101300X

Extended X‐ray absorption fine structure (EXAFS) is a comprehensive and usable method for characterizing the structures of various materials, including radioactive and nuclear materials. Unceasing discussions about the interpretation of EXAFS results for actinide nanoparticles (NPs) or colloids were still present during the last decade. In this study, new experimental data for PuO2 and CeO2 NPs with different average sizes were compared with published data on AnO2 NPs that highlight the best fit and interpretation of the structural data. In terms of the structure, PuO2, CeO2, ThO2, and UO2 NPs exhibit similar behaviors. Only ThO2 NPs have a more disordered and even partly amorphous structure, which results in EXAFS characteristics. The proposed new core‐shell model for NPs with calculated effective coordination number perfectly fits the results of the variations in a metal–metal shell with a decrease in NP size. New experimental EXAFS results for PuO2 and CeO2 nanoparticles in the size range of 2 nm were compared with published data for other lanthanide and actinide dioxides. A conceptual core‐shell model with a calculated effective coordination number is proposed to fit the changes in EXAFS.