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 Th1–xUxO2 (x = 0.25, 0.5, 0.75) solid solution was probed by the Th L3 edge high-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) collected at the Lβ5 emission line, which cannot be obtained by conventional X-ray absorption methods. The detected CEF split between the 6d eg and t2g orbitals in ThO2 consisting of ordered Th–O8 cubes with cubic symmetry is ∼3.5 eV for the Th4+ 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–O8 cubes in the Th1–xUxO2 mixed oxides. The lower symmetry of the Th–O8 cube induced by the incorporated U tends to reduce the local crystal-field around Th4+ as well as the hybridization of Th 6t2g–O 2p which is mainly responsible for the covalent property of the Th–O bond. The phenomenon is noticeable in Th0.25U0.75O2, whose CEF splitting is decreased by approximately 10%, and covalent mixing between Th 6d t2g and O 2p orbitals is substantially reduced compared to that of pure ThO2.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".