Substitutional Cu Doping at Ca and Nb Sites in Ba<sub>3</sub>CaNb<sub>2</sub>O<sub>9</sub> Toward Improved Photoactivity–A First-Principles HSE06 Study
Bibliographic record
Abstract
Seeking tenable and sustainable alternatives for clean energy harvesting, artificial photosynthesis has emerged as a realm of research. We have investigated the effects of Cu doping at Ca and Nb sites in Ba 3 CaNb 2 O 9 (BCN) on magneto-optoelectronic properties through Density Functional Theory studies, employing the HSE06 hybrid functional to guide rational syntheses. Our calculations show that while Cu replacement of a Ca atom requires lower formation energy than replacing an Nb atom, oxygen vacancies (O V ) gradually reduce this to a large extent within the thermodynamic formability window when placed at the nearest O site, promoting Nb replacement. Cu doping at the Nb site substantially narrows the band gap, inducing the absorption of visible photons as the dopant concentration increases, while the placement of O V at CuO 6 causes gradual blue shifts. Cu doping induces weak electron polaron formation in the CuO 6 unit due to net spin polarization in Cu d states, while the placement of the O V annihilates it, albeit without reducing the oxidation state of Cu due to strong charge delocalization. Cu doping at the Nb site significantly improves the optical activity vis-à-vis pure BCN in the visible light region, especially ∼2–3 eV, resulting in promising candidates for photoelectrochemical catalysts.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".