Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors <i>RE</i><sub>2</sub>Sn(S<sub>1–<i>x</i></sub>Se<sub><i>x</i></sub>)<sub>5</sub> (<i>RE</i> = La, Ce; <i>x</i> = 0–0.8)
Bibliographic record
Abstract
The ternary rare-earth sulfides RE 2 SnS 5 ( RE = La–Nd) and the partial solid solutions RE 2 Sn(S 1– x Se x ) 5 ( RE = La, Ce; x = 0–0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La 2 SnS 5 -type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing Sn Ch 6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE 2 Sn(S 1– x Se x ) 5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE 2 SnSe 5 do not form. Solid-state 119 Sn NMR spectra confirmed the nonrandom distribution of SnS 6– n Se n local environments, which could be resolved into individual resonances. The Raman spectra of RE 2 SnS 5 compounds show an intense peak at 307–320 cm –1 assigned to a symmetric A 1g mode, which is dominated by Sn–S bonds; the Raman peak intensities varied with Se substitution in La 2 Sn(S 1– x Se x ) 5 . Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE 2 SnS 5 (0.7 eV) but they gradually decrease with greater Se substitution in RE 2 Sn(S 1– x Se x ) 5 (0.7–0.4 eV).
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".