Short-range constraints on chemical and structural variations in bavenite
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Bibliographic record
Abstract
Abstract Bavenite is an orthorhombic calcium beryllium aluminosilicate, a ≈ 23.2, b ≈ 5.0, c ≈ 19.4 Å, V ≈ 2250 Å 3 , Z = 4, that crystallizes in the space group Cmcm . The crystal structures of 24 bavenite samples from various localities worldwide were refined to R1 values from 2.4 to 7.5% based on ∼1330 unique reflections collected with Mo- Kα X-radiation on a Bruker P 4 CCD single-crystal diffractometer. The composition of each crystal was determined by electron microprobe analysis. There is extensive solid-solution in bavenite according to O(2) OH – + T(4) Si 4+ + T(3) Be 2+ ⇌ O(2)O 2– + T(4) Al 3+ + T(3) Si 4+ , such that the general formula may be written Ca 4 Be x Si 9 Al 4–x O 28–x (OH) x , where x ranges from 2.00 to ∼3.00 a.p.f.u. Small amounts of additional Be may be incorporated into bavenite via the substitution T(3) Be + O(2) OH – + Na + T(4) Si 2 ⇌ T(3) Si + O(2) O 2– + Ca + T(4) Al 2 . Local (short-range) bond-valence considerations indicate that Short-Range Order (SRO) should be extensive in the bavenite structure, and this is confirmed by Fourier Transform Infrared (FTIR) spectroscopy in the principal OH-stretching region and by 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. Short-range bond-valence considerations indicate that the T(3)–T(4)–T(3)–T(4) rings of the framework can incorporate any short-range arrangement of cations consonant with their site populations [ T(3) = Be,Si; T(4) = Si,Al], and 27 Al MAS NMR spectroscopy confirms this, showing the presence of the local clusters T(3) Be– T(4) Al– T(3) Be, T(3) Si– T(4) Al– T(3) Be and T(3) Si– T(4) Al– T(3) Si. Incorporation of Be at the T(3) site is accompanied by local replacement of O 2– by (OH) – at the O(2) site and hydrogen bonding to the adjacent O(3) anion; the latter promotes Be → Si substitution at the T (3) tetrahedron adjacent in the b direction. T (3)– T (4)– T (3)– T (4) rings link in the c direction through a T (3)–(1)–(3) linkage [ T (1) = Si]. Local bond-valence considerations show that occupancy of both T (3) tetrahedra by Be violates the valence-sum rule, and that the linkage T(3) Be– T(1) Si– T(3) Si provides the constraint whereby Be does not exceed 3 a.p.f.u. in bavenite when incorporated via the substitution O(2) OH – + T(4) Si 4+ + T(3) Be 2+ ⇌ O(2) O 2– + T(4) Al 3+ + T(3) Si 4+ .
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.004 | 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 it