Crystal structure of isolueshite and its synthetic compositional analogue
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Bibliographic record
Abstract
The crystal structure of isolueshite, a recently described member of the perovskite group from the Khibina complex (Russia), was refined by single-crystal methods in the space group Pm33m [a = 3.909(1) A] to R = 0.031 and wR = 0.061. The previously proposed cubic symmetry of isolueshite was confirmed. In contrast to the known perovskite-group minerals crystallizing with the cubic symmetry, isolueshite shows a disordered arrangement of oxygen atoms in a Pm33m -type cell. In isolueshite, the oxygen atoms are disordered from their “ideal” site at 3 c (1/2, 0, 1/2) over four 12 h sites ( x , 0, 1/2) with a refined x of 0.579(5). The refinement was based on the structural formula (Na 0.75 La 0.19 Ca 0.06 ) ∑1.00 (Nb 0.50 Ti 0.50 ) ∑1.00 O 3.00 closely corresponding to the empirical formula of the mineral. The presence of hydroxy1 groups in the structure of isolueshite was confirmed by infrared spectroscopy (absorption lines at 3450 cm −1 and 1080 cm −1 ). Structural formulae of the mineral accounting for the presence of (OH) −1 groups are given. A synthetic compound of the composition (Na 0.75 La 0.25 ) (Nb 0.50 Ti 0.50 )O 3 was prepared using the ceramic technique (final heating at 1200°C), and shown not to crystallize with cubic symmetry. The crystal structure of this compound is best refined (Rietveld method) in orthorhombic symmetry [ Cmcm, a = 7.7841(9), b = 7.8045(2), c = 7.7831 (9) A]. This structure is derived from the ideal perovskite lattice ( Pm3m ) by rotation of the (Nb,Ti)O 6 octahedra about two tetrad axes of the cubic subcell (tilt system a 0 b + c). Our data and, in particular, the presence of oxygen disorder (incongruent octahedral tilting) in the structure of isolueshite, suggest that stabilization of the cubic symmetry of this mineral may be controlled by thermodynamic or kinetic factors (crystallization temperature, pressure or cooling rate), rather than by the isomorphic substitutions involving La and Ti. Hence, isolueshite should probably be considered a quenched or “frozen” polymorph of NaNb0 3 .
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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) | 0.003 | 0.000 |
Machine scores (provisional)
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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