Fabrication and properties of Bi2S3-xSex thermoelectric polycrystals

Bi₂S_3-x Se_x (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 Bi₂S_2.85Se_0.15 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 Bi₂S_2.85Se_0.15. The thermal conductivity of Bi₂S_3-xSe_x 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 Bi₂S_2.8Se_0.15 sample, which is about 1.6 times that (0.11) of the pristine Bi₂S₃ sample.