THE ORTHORHOMBIC STRUCTURE OF CaCO3, SrCO3, PbCO3 AND BaCO3: LINEAR STRUCTURAL TRENDS
Bibliographic record
Abstract
The crystal structures of four isostructural orthorhombic carbonates, CaCO{sub 3} (aragonite), SrCO{sub 3} (strontianite), PbCO{sub 3} (cerussite), and BaCO{sub 3} (witherite), were obtained by Rietveld refinements using data acquired by synchrotron high-resolution powder X-ray diffraction (HRPXRD). For BaCO{sub 3}, powder neutron-diffraction data were obtained and refined by the Rietveld method. For aragonite, we also carried out a refinement of the structure by single-crystal X-ray diffraction. These carbonates belong to the space group Pmcn, with Z = 4. The CO{sub 3} group is slightly non-planar, and the two independent C-O distances are slightly different. The CO{sub 3} group becomes more symmetrical and less aplanar from CaCO{sub 3} to BaCO{sub 3} (M{sub radii}{sup 2+}: Ca and distances, average angle, and aplanarity. These linear trends are the result of the effective size of the divalent ionic radius of the M cations thatmore » are coordinated to nine oxygen atoms. The geometrical features of the CO{sub 3} group can be obtained reliably only by using neutron-diffraction data, especially in the presence of other heavy atoms.« less
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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 | 0.001 |
| 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) | 0.002 | 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".