Modulation of transport properties via S/Br substitution: solvothermal synthesis, crystal structure, and transport properties of Bi13S17Br3

Abstract

The solvothermal synthetic exploration of the Bi–S–halogen phase space resulted in the synthesis of two bismuth sulfohalides with common structural motifs. Bi₁₃S₁₈I₂ was confirmed to have the previously reported composition and crystal structure. In contrast, the bromide analogue was shown to have a formula of neither Bi₁₉S₂₇Br₃ nor Bi₁₃S₁₈Br₂, 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 Bi₁₃S₁₇Br₃ due to the partial S/Br substitution in the framework. Bi₁₃S₁₈I₂ and Bi₁₃S₁₇Br₃ 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, Bi₁₃S₁₇Br₃ 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.