Thermoelectric and mechanical properties of Bi2S3−xSex polycrystals

Bi 2 S 3 has the advantages of nontoxic and low-cost components, high Seebeck coefficient, and intrinsically low thermal conductivity, making it a promising thermoelectric material. However, its poor electrical conductivity limits its thermoelectric performance across all temperature ranges. To improve the conductivity of Bi 2 S 3 -based thermoelectric materials, Se, a Group VIA element similar to S, was chosen as an effective doping element to synthesise Bi 2 S 3−x Se x (x = 0, 0.1, 0.3, 0.5) bulk material via melting and spark plasma sintering. The room-temperature electrical conductivity of Bi 2 S 2.7 Se 0.3 was approximately 24 S·cm −1 , which is two orders of magnitude higher than that of pristine Bi 2 S 3 . At 623 K, Bi 2 S 2.5 Se 0.5 exhibited an ultralow thermal conductivity of 0.5 µW·m −1 ·K −1 . Thus, Se doping not only enhanced the electrical conductivity of Bi 2 S 3 but also increased phonons scattering through Se substitution and interstitial Se, which significantly reduced the lattice thermal conductivity of Bi 2 S 3 . Consequently, the Bi 2 S 2.7 Se 0.3 sample achieved an optimal ZT value of approximately 0.16 at 573 K, which is four times higher than that of the pristine Bi 2 S 3 sample.