Transport Properties of Bi2S3 and the Ternary Bismuth Sulfides KBi6.33S10 and K2Bi8S13

Abstract

We have studied transport properties (resistivity, Hall effect, thermopower, and thermal conductivity) of Bi 2 S 3 and two new ternary bismuth sulfides, KBi 6.33 S 10 and K 2 Bi 8 S 13, to explore their potential for thermoelectric applications. While both Bi 2 S 3 and K 2 Bi 8 S 13 display an essentially metallic conduction, KBi 6.33 S 10 has a distinctly semiconducting character. From the Hall measurements it follows that the dominant carriers in all three compounds are electrons and that the carrier density in K 2 Bi 8 S 13 is almost 2 orders of magnitude larger than in Bi 2 S 3 and KBi 6.33 S 10 over the whole temperature range from 4 to 300 K. While the room temperature thermopowers of KBi 6.33 S 10 and K 2 Bi 8 S 13 are comparable (∼−100 μV/K), the thermopower of Bi 2 S 3 is a factor of 3 larger. All three compounds are poor conductors of heat, in particular the thermal conductivity of KBi 6.33 S 10 is some 25% lower than the thermal conductivity of Bi 2 Te 3, the benchmark thermoelectric material. To make these materials useful thermoelectrics, ways must be found how to significantly increase their electrical conduction while preserving the reasonably large thermopower and low thermal conductivity.