Elucidation of the Na<sub>2/3</sub>FePO<sub>4</sub> and Li<sub>2/3</sub>FePO<sub>4</sub> Intermediate Superstructure Revealing a Pseudouniform Ordering in 2D
Bibliographic record
Abstract
Based on TEM, synchrotron X-ray diffraction, DFT calculations, and Mössbauer spectroscopy, a unified understanding of the Na and Li intercalation process in FePO4 is proposed. The key to this lies in solving the highly sought-after intermediate A(2/3)FePO4 (A = Na, Li) superstructures that are characterized by alkali ions as well as Fe(II)/Fe(III) charge orderings in a monoclinic three-fold supercell. Formation energies and electrochemical potential calculations confirm that Na(2/3)FePO4 and Li(2/3)FePO4 are stable and metastable, respectively, and that they yield insertion potentials in fair agreement with experimental values. The 2/3 Na(Li) and 1/3 vacancy sublattice of the intermediate phases forms a dense (101)(Pnma) plane in which the atom/vacancy ordering is very similar to that predicted for the most uniform distribution of 1/3 of vacancies in a 2D square lattice. Structural analysis strongly suggests that the key role of this dense plane is to constrain the intercalation in the diffusion channels to operate by cooperative filling of (bc)(Pnma). From a practical point of view, this generalized mechanism highlights the fact that an interesting strategy for obtaining high-rate FePO4 materials would consist in designing grains with an enhanced (101) surface area, thereby offering potential for substantial improvements with respect to the performance of rechargeable Li and Na batteries.
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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) | 0.001 | 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".