Bx. Chen et al., TRANSPORT PROPERTIES,OF BI2S3 AND THE TERNARY BISMUTH SULFIDES KBI6.33S10 AND K2BI8S13, Chemistry of materials, 9(7), 1997, pp. 1655-1658
We have studied transport properties (resistivity, Hall effect, thermo
power, and thermal conductivity) of Bi2S3 and two new ternary bismuth
sulfides, KBi6.33S(10) and K2Bi8S13, to explore their potential for th
ermoelectric applications. While both Bi2S3 and K2Bi8S13 display an es
sentially metallic conduction, KBi6.33S10 has a distinctly semiconduct
ing character. From the Hall measurements it follows that that dominan
t carriers in all three compounds are electrons and that the carrier d
ensity ih K2Bi8S13 is almost 2 orders of magnitude larger than in Bi2S
3 and KBi6.33S10 over the whole temperature range from 4 to 300 K. Whi
le the room temperature thermopowers of KBi6.33S10 and K2Bi8S13 are co
mparable (similar to-100 mu V/K), the thermopower of Bi2S3 is a factor
of 3 larger. All three compounds are poor conductors of heat, in part
icular the thermal conductivity of KBi6.33S10 is some 25% lower than t
he thermal conductivity;of Bi2Te3, the benchmark thermoelectric materi
al. To make these materials useful thermoelectrics, ways must be found
how to significantly increase their electrical conduction while prese
rving the reasonably large thermopower and low thermal conductivity.