The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO₂

Abstract

The structuralc haracterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non-homogeneous samples with NPs less than 3nm. By combining high-energyX-ray scattering (HEXS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD XANES) analysis,w eh ave characterised for the first time both the short-and mediumrange order of ThO 2 NPs obtained by chemicalp recipitation. By using this methodology,anovel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution functionr evealed ah igh concentration of ThO 2 small units similart ot horium hexamer clusters mixed with1nm ThO 2 NPs in the initial steps of formation. Drying the precipitates at around1 50 8Cp romoted the recrystallisation of the smallest units into more thermodynamically stable ThO 2 NPs. HERFD XANES analysis at the thorium M 4 edge, ad irect probe for fs tates, showed variations that we have correlated with the breakdown of the local symmetry aroundt he thorium atoms, which most likely concerns surface atoms. To gether,H EXS and HERFD XANES are ap owerful methodology for investigatinga ctinideN Ps and their formation mechanism.

High-energy resolution X-ray spectroscopy at actinide M4,5 and ligand K edges: what we know, what we want to know, and what we can know

“…One of the crucial aspects here is that the physical and chemical properties of the materials are changing as it comes to the nanoscale. HERFD methodology at the actinide M 4,5 edges has been successfully used in recent electronic structure investigations of the UO 2 66 , ThO 2 82 and PuO 2 61,63 nanoparticles (NPs). Authors experimentally traced the route of the Pu(VI) to PuO 2 NPs transformation as a two-step process 61 .…”

Probing the Local Coordination of Hexavalent Uranium and the Splitting of 5f Orbitals Induced by Chemical Bonding

“…9 A similar discrepancy between FDMNES calculations and data has been observed by the at the M 4 edge of ThO 2 . 22 Additionally, differences between the real local structure of U compared to the average structure represented by the crystal structure may also affect the calculated spectra. Indeed, EXAFS showed that for Sr 3 UO 6 two U−O distances are slightly shorter compared to the value from powder XRD results (2.04 Å instead of 2.07 Å), 25 and the intensity of the first peak in the XANES simulation increases if the local structure is modified according to EXAFS results.…”

Thermal Energy Transport in Oxide Nuclear Fuel

“…Here we provide a brief review of two experimental techniques used to gleam information about sub-nanometer defects. Point defects in oxides such as UO2, CeO2, and ThO2 have been extensively characterized using light source techniques [322,332,333,334,335,336,337,338,339,340,341,342,343,344]. This field of study has recently been review by Lang, et al [345].…”