Chemistry and Technology of Samarium Monosulfide
Samarium monosulfide SmS (Fm3m, а = 5.967 Å, ΔЕ = 0.23 V, n = 1020 cm–1, σ = 500 Ω–1 cm–1, α = 350 μВ/K) is a thermoelectric material (Z>1) and, at the same time, a pressure-sensitive material (K≥40–50). Samarium monosulfide is a daltonide phase with a solid solution whose extent is mostly in the...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
al-Farabi Kazakh National University
2016-01-01
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| Series: | Eurasian Chemico-Technological Journal |
| Online Access: | http://ect-journal.kz/index.php/ectj/article/view/191 |
| Summary: | Samarium monosulfide SmS (Fm3m, а = 5.967 Å, ΔЕ = 0.23 V, n = 1020 cm–1, σ = 500 Ω–1 cm–1, α = 350 μВ/K) is a thermoelectric material (Z>1) and, at the same time, a pressure-sensitive material (K≥40–50). Samarium monosulfide is a daltonide phase with a solid solution whose extent is mostly in the range of cationic vacancies: Sm1+x S1-x2x (x = 0–0.035; 1750 K). The congruent melting temperature of SmS is 2475 K. In the Sm–S system, Sm3S4 crystallizes from melt without change in composition. Samarium monosulfide thermally dissociates to Sm3S4 and Sm. Largescale SmS lots are produced from samarium and sulfur. Synthesis is carried out in sealed-off silica glass ampoules at 500–1350 K followed by heat treatment in tantalum crucibles at 1500–2400 K. The reaction of metal samarium with sulfur results in the formation of sulfide phases that coat the samarium surface in the following order: SmS, Sm3S4, Sm2S3, and SmS2. Subsequent annealing at 1500–1800 K provides SmS yields up to 96–97 mol %. Equilibrium minor phases for SmS are Sm3S4, Sm2О2S, and Sm. X-ray amorphous SmS was prepared by reacting organic samarium compounds with sulfur or H2S. The samarium (+2) oxidation state determines the chemical specifics of SmS. 90–120 μm SmS powders are thermally hydrolyzed starting at 600 K with Н2 evolution and oxidize starting at 520 K to yield Sm3S4 and then Sm2О2S phases. A 90–120 μm SmS fraction for film deposition by flash evaporation is prepared by milling annealed SmS samples. Tablets 75 mm in diameter for use in magnetron sputtering are pressed from a <60-μm fraction. |
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| ISSN: | 1562-3920 2522-4867 |