The solvothermal synthetic exploration of the Bi–S–halogen phase space resulted in the synthesis of two bismuth sulfohalides with common structural motifs. Bi 13 S 18 I 2 was confirmed to have the previously reported composition and crystal structure. In contrast, the bromide analogue was shown to have a formula of neither Bi 19 S 27 Br 3 nor Bi 13 S 18 Br 2 , in contrast to the previous reports. The composition, refined from single crystal X-ray diffraction and confirmed by elemental analysis, high-resolution powder X-ray diffraction, and total scattering, is close to Bi 13 S 17 Br 3 due to the partial S/Br substitution in the framework. Bi 13 S 18 I 2 and Bi 13 S 17 Br 3 are n -type semiconductors with similar optical bandgaps of ∼0.9 eV but different charge and heat transport properties. Due to the framework S/Br disorder, Bi 13 S 17 Br 3 exhibits lower thermal and electrical conductivities than the iodine-containing analogue. The high Seebeck coefficients and ultralow thermal conductivities indicate that the reported bismuth sulfohalides are promising platforms to develop novel thermoelectric materials.
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Ultralow thermal conductivity through the interplay of composition and disorder between thick and thin layers of makovickyite structure
Here we report the synthesis and characterization of three quaternary complex chalcogenides, Ag 0.72 Bi 5.48 Cu 0.88 S 9 (I), Ag 0.70 Bi 5.30 Cu 1.3 S 9 (II), Ag 0.34 Bi 4.54 Cu 1.98 PbS 9 (III). All the compounds in this homologous series crystallize in the C 2 /m space group and can be described as Pavonite structures. This structure type consists of alternating NaCl-like layers with varied thickness ( n P ), separated by a pair of square pyramids. All the compounds reported here are synthetic analogues of the n = 4 pavonite family and are known as makovickyite minerals. Compounds I–III possess complex crystal structures, consisting of mixed occupancies of Bi/Ag/Pb sites, as well as partially occupied Cu sites. These intrinsic assets lead to ultra-low lattice thermal conductivities, in the range of 0.75–0.42 Wm −1 K −1 from 300–500 K, and make these materials promising candidates for thermoelectric applications. All three structures exhibit very narrow indirect band gaps of less than 0.5 eV as confirmed by DRS measurements. Charge transport properties are consistent with n-type semiconducting behavior with moderate electrical conductivities and large Seebeck coefficients. Low temperature electrical resistivity and Seebeck coefficient measurements are also performed on II. A promising figure of merit, zT , of 0.09 for I and II, 0.11 for III can be achieved at 475 K.
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- Award ID(s):
- 2001156
- NSF-PAR ID:
- 10324456
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 9
- Issue:
- 34
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 11207 to 11215
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A redox‐neutral
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1tc02173g
