The application of HEXS and HERFD XANES for accurate structural characterization of actinide nanomaterials: application to ThO2

TL;DR

This study combines HEXS and HERFD XANES techniques to accurately characterize the structure and formation process of ThO2 actinide nanoparticles, revealing insights into their short- and medium-range order and surface atom symmetry.

Contribution

It introduces a novel combined methodology using HEXS and HERFD XANES for detailed structural analysis of actinide nanoparticles, especially during their formation.

Findings

ThO2 NPs initially consist of Th hexamer clusters and 1 nm particles.

Drying induces recrystallization into more stable NPs.

HERFD XANES detects local symmetry changes around Th atoms.

Abstract

Structural characterization of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non-homogeneous samples with NPs below 3 nm. By combining High Energy X-ray Scattering (HEXS) and High-Energy-Resolution Fluorescence Detected X-ray Near-Edge Structure (HERFD XANES), we characterized for the first time both short- and medium-range order of ThO2 NPs obtained by chemical precipitation. With this methodology, a novel insight into the structure of NPs at different steps of their formation process is achieved. The Pair Distribution Function (PDF) reveals a high concentration of ThO2 small units similar to Th hexamer clusters mixed with 1 nm ThO2 NPs in the initial steps of formation. Drying the precipitates at 150 C promotes recrystallization of the smallest units into more thermodynamically stable ThO2 NPs. HERFD XANES at Th M4 edge, a direct probe of the f states, shows variations that we correlate to the break of the local symmetry around Th atoms, which most likely concerns surface atoms. Together, HEXS and HERFD are a powerful methodology to investigate actinide NPs and their formation mechanism.