Electron paramagnetic resonance spectroscopic study of synthetic fluorapatite: Part I. Local structural environment and substitution mechanism of Gd <sup>3+</sup> at the Ca2 site
Bibliographic record
Abstract
Gd-doped fluorapatite (1.2 ± 0.2 wt% Gd 2 O 3 ), synthesized from CaF 2 -rich melts, has been investigated as single crystals and powder samples by using X-band (~9.4 GHz) electron paramagnetic resonance (EPR) spectroscopy at -295 and 120 K. The well-resolved X-band EPR spectra yielded a previously unreported type of Gd 3+ center “a” (S = 7/2) and also suggested the possible presence of a second and partly resolved type of Gd 3+ center “b.” In particular, the single-crystal X-band EPR spectra of center “a” from three orthogonal-rotation planes allowed determination of the spin-Hamil- tonian parameters, including the spin terms of type BS (matrix g) and S 2 (matrix D) and the parameters associated with the high-spin terms of type S 4 and S 6 as well as BS 3 and BS 5 . The validity of the parameters has been confirmed by agreement between observed and simulated EPR spectra for both single crystals and powder samples. The principal values of the matrices g and D indicate that the local symmetry of center “a” in the X-band EPR spectra is rhombic. The principal axis directions of the D suggest that this Gd 3+ center arises from a substitution of Gd 3+ ion into the Ca2 type of site. This assignment is supported by the results of a pseudo-symmetry analysis using the S 4 parameters, e.g., the calculated twofold pseudosymmetry axis coincides with the twofold rotoinversion axis of the Ca2 site. The local structural environment of this Gd 3+ ion suggests that the ion is incorporated via the mechanism Gd 3+ + 0 2- ↔ Ca 2+ + F-.
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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) | 0.000 | 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 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".