Uranium-Induced Changes in Crystal-Field and Covalency Effects of Th<sup>4+</sup> in Th<sub>1–<i>x</i></sub>U<sub><i>x</i></sub>O<sub>2</sub> Mixed Oxides Probed by High-Resolution X-ray Absorption Spectroscopy
Bibliographic record
Abstract
Knowledge of the local Th structure is a prerequisite for a better understanding of the physicochemical properties of the thorium-based mixed oxides (Th-MOX) involved in the Th-based nuclear fuel cycle. The crystalline electric field (CEF) splitting of the 6d shell in Th 1– x U x O 2 ( x = 0.25, 0.5, 0.75) solid solution was probed by the Th L 3 edge high-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) collected at the L β5 emission line, which cannot be obtained by conventional X-ray absorption methods. The detected CEF split between the 6d e g and t 2g orbitals in ThO 2 consisting of ordered Th–O 8 cubes with cubic symmetry is ∼3.5 eV for the Th 4+ ion. Because the split peaks of the white line corresponding to the crystal-field splitting of the unoccupied 6d states were resolved in the HERFD-XANES spectra, the analysis of these split peaks combined with first-principles calculations revealed that an increase of the U content involves the distortion of the Th–O 8 cubes in the Th 1– x U x O 2 mixed oxides. The lower symmetry of the Th–O 8 cube induced by the incorporated U tends to reduce the local crystal-field around Th 4+ as well as the hybridization of Th 6t 2g –O 2p which is mainly responsible for the covalent property of the Th–O bond. The phenomenon is noticeable in Th 0.25 U 0.75 O 2, whose CEF splitting is decreased by approximately 10%, and covalent mixing between Th 6d t 2g and O 2p orbitals is substantially reduced compared to that of pure ThO 2 .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".