Analysis of Metal Site Preference and Electronic Structure of Brownmillerite-Phase Oxides (A<sub>2</sub>B<i>′</i><sub><i>x</i></sub>B<sub>2−<i>x</i></sub>O<sub>5</sub>; A = Ca, Sr; B′/B = Al, Mn, Fe, Co) by X-ray Absorption Near-Edge Spectroscopy
Bibliographic record
Abstract
X-ray absorption near-edge spectroscopic (XANES) measurements of the Fe and Co K-edges for a series of Brownmillerite-type transition-metal oxides (A 2 B′ x B 2− x O 5; A = Ca, Sr; B′/B = Al, Mn, Fe, Co) have been made. In these compounds, the metal atoms are present in both octahedral and tetrahedral coordination environments. The spectra were interpreted with the aid of electronic structure calculations. Significant changes in intensity and energy were observed in the Fe K-edge spectra as the average Fe 3+ coordination number (CN) was changed from 5.5 (Ca 2 AlFeO 5 ) to 4.2 (Ca 2 FeMnO 5 ). In Ca 2 Co x Fe 2− x O 5, the Fe K- and Co K-edge XANES spectra indicated that Fe has a slight octahedral site preference in these series. This confirmed that size effects play a significant role in controlling the site preference of metal atoms in these compounds. The change in the average Fe CN with Co substitution was examined by analysis of a 3D plot, which compared all of the changes observed in the spectra. This type of analysis gives an accurate depiction of the change in Fe CN as compared to standard materials. The Fe K-edge peak intensities in Ca 2− y Sr y Fe 2 O 5 decreased with higher values of y, a result of decreased Fe 4p(3d)−O 2p overlap with increasing Sr concentration.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".