Electron paramagnetic resonance spectroscopic study of synthetic fluorapatite: Part II. Gd <sup>3+</sup> at the Ca1 site, with a neighboring Ca2 vacancy
Bibliographic record
Abstract
A W-band (94 GHz) electron paramagnetic resonance (EPR) study of synthetic fluorapatite with 57 ± 4 ppm Gd has been made on single crystals at ~287 K. The spectra disclosed the presence of a previously unreported type of Gd 3+ center denoted by “b” herein (S = 7/2), in addition to the Gd 3+ center “a” assigned to the Ca2 site using the results of a previous X-band (9.5 GHz) EPR study (Chen et al. 2002). In particular, the single-crystal W-band EPR spectra from three orthogonal-rotation planes allowed determination of an appropriate spin-Hamiltonian for center “b,” 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 . Agreement between the observed and simulated single-crystal spectra confirmed the validity of the spin-Hamiltonian analysis.β The principal values of the matrices g and D [e.g.. D/g e β e = 1069.2( 1) G and E/g e β e = 52.4(3) G] suggest a considerably distorted rhombic local environment for the Gd 3+ ions in center “b.” The principal directions of D suggest that “b” corresponds to Gd 3+ at the Ca 1 site. This site assignment is supported by a pseudo-symmetry analysis of the term S 4 , i.e., approximate matching of the directions of the calculated pseudo-symmetry axes to the bond directions and face normals of the coordination polyhedron of the ideal Cal site. The data suggest that the incorporation of Gd 3+ into the Cal site is achieved by a coupled substitution (2Gd 3+ + □ ↔ 3Ca 2+ ) involving a Ca 2+ vacancy □ and that the vacancy is located at a next-nearest-neighbor Ca2 site, resulting in a Gd 3+ - - □ - Gd 3+ arrangement, with the cations well separated.
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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".