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 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) | 0.002 | 0.002 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.003 |
| 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 itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
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".