Fabrication and properties of Bi2S3−xSex thermoelectric polycrystals

• Bi2S3−xSex (x=0, 0.05, 0.15, 0.30) alloys were fabricated by MA and SPS technique.
• Se is an effective n-type doping element for Bi2S3 polycrystals.
• Thermoelectric efficiency ZT is maximized for the Bi2S2.85Se0.15 sample at 573 K.

Bi2S3−x Sex (x=0–0.3) polycrystals were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The phase, microstructure, electrical and thermal transport properties were investigated with a special emphasis on the influence of Se content. All the samples were indexed as single phase with an orthorhombic symmetry. Optimizing the Se content greatly improves the electrical conductivity, achieving a peak value of 750 Sm−1 at 573 K for the Bi2S2.85Se0.15 composition. The absolute value of Seebeck coefficient shows an inversely varying trend to the electrical conductivity with Se content, whereby a power factor at 573 K is enhanced from 91 µ Wm−1 K−2 for pristine Bi2S3 to 124 µ Wm−1 K−2 for Bi2S2.85Se0.15. The thermal conductivity of Bi2S3−xSex ranges from 0.44 to 0.73 Wm−1 K−1 at the temperature from 323 to 573 K. A maximum ZT value reached 0.16 at 573 K for the Bi2S2.8Se0.15 sample, which is about 1.6 times that (0.11) of the pristine Bi2S3 sample.