CRYSTAL STRUCTURE OF COPPER-RICH UNSUBSTITUTED TENNANTITE, Cu12.5As4S13
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Bibliographic record
Abstract
The crystal structure of a Cu-rich tennantite from Cerro Atajo, province of Catamarca, northwestern Argentina, has been refined using single-crystal data (MoKX-ray diffraction, CCD detector, R1 = 0.03). It crystallizes in space group I3m, with a = 10.1756(9) A. The X-ray-diffraction analysis led to the formula Cu12.5(As0.98Sb0.02)� 4S13, in full agreement with the electron- microprobe data and the unit-cell parameter. Cu-rich tennantite shows all structural features of tetrahedrite and tennantite, but it contains a partly occupied triangular Cu2A position, accompanied by a new site, Cu2B, coordinated tetrahedrally to three S and one As atom. This finding is in contrast to Cu-rich tetrahedrite, where partial occupancy and redistribution of Cu are associated with the Cu1 site. Atoms Cu2A and Cu2B form, respectively, an octahedron and a Laves polyhedron around the S2 site, a situation similar to Te3 coordination in � -Ag8SiTe6 and � -Ag8GeTe6. On the basis of bond lengths, we contend that the Cu 2+ necessary to balance the formula resides primarily at the Cu1 site. The electron density shows a dynamic disorder between closely separated Cu2A and Cu2B sites, which, together with available vacancies at these positions, suggests that Cu-rich tennantite is an ionic conductor even at room temperature. The Cu-rich tennantite is a rare case of formation from late hydrothermal solutions devoid of ubiquitous Fe, Zn and other divalent elements, which usually enter tennantite as electron donors.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 it