The structural relation between the new synthetic silicate K2ScFSi4O10 and narsarsukite, Na2(Ti,Fe3+)(O,F)Si4O10
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Bibliographic record
Abstract
During investigations of the system Sc 2 O 3 -Al 2 O 3 -TiO 2- SiO 2 , a new, unusual silicate, K 2 ScFSi 4 O 10 , was synthesised as colourless pseudo-cuboctahedral crystals from a KF-MoO 3 flux. The crystal structure was determined from single-crystal X-ray diffraction data (Mo- Ka radiation, CCD area detector, 2𝛉 max = 65°, R int = 1.07 %) and refined in space group I4/m (no. 87) to R 1( F ) = 1.46% and w R2 all = 4.15% using 976 ‘observed’ reflections with F 0 > 40( F 0 ). Unit-cell parameters are: a = 11.207(2), c = 8.166(2) A, V = 1025.6(4) A 3 , Z = 4. The crystal studied is merohedrally twinned with twin plane {110}, and shows pseudo-symmetry I4/mmm. , The structure contains infinite chains of corner-sharing, nearly regular ScO 4 F 2 octahedra [ d av (Sc-O) = 2.071 A, d av (Sc-F) = 2.042 A] connected via shared F atoms along [001]. These octahedral chains share their O atoms with tubular [001] silicate chains built from four-membered silicate rings. The latter are built from one crystallographically unique, distorted SiO 4 tetrahedron with d av (Si-O) = 1.617 A. The resulting three-dimensional framework hosts voids occupied by a unique, eight-coordinated K atom. K 2 ScFSi 4 O 10 is isotypic with narsarsukite Na 2 (Ti, Fe 3+ )(O, F)Si 4 O 10 , but, although their topologies are basically identical, there exist differences which cause the merohedral twinning and pseudo-holohedry (pseudo- I4/mmm ) of K 2 ScFSi 4 O 10 : the presence of the larger K atom causes a considerable rotation of the octahedral units around [001] and a distinct rearrangement of the framework voids, both leading to the presence of a pseudo-mirror plane {110}. In narsarsukite, no such twinning is possible, as demonstrated by a careful reinvestigation of the crystal structure of a narsarsukite crystal from Mont Saint Hilaire, Canada, which confirmed a previous structure determination. The crystal-chemical relations between K 2 ScFSi 4 O 10 and KTiOPO 4 -type A ScFAsO 4 ( A = Rb, Cs) and other compounds and minerals containing trans or cis MO 4 F 2 ( M = Cr, Al, Fe) octahedra are pointed out. A structure determination of K 2 ScFSi 4 O 10 at 120 K revealed no significant changes of the atomic arrangement. The shrinkage was distinctly stronger along [001] than that along [100].
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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 | 0.001 | 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 | 0.001 | 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 it