Enhancement of Thermoelectric Properties in Cold Pressed Nickel Doped Bismuth Sulfide Compounds

Nanostructured Ni doped Bi 2 S 3 (Bi 2−x Ni x S 3 , 0 ≤ x ≤ 0.07) is explored as a candidate for telluride free thermoelectric material, through a combination process of mechanical alloying with subsequent consolidation by cold pressing followed with a sintering process. The cold pressing method was found to impact the thermoelectric properties in two ways: (1) introduction of the dopant atom in the interstitial sites of the crystal lattice which results in an increase in carrier concentration, and (2) introduction of a porous structure which reduces the thermal conductivity. The electrical resistivity of Bi 2 S 3 was decreased by adding Ni atoms, which shows a minimum value of 2.35 × 10 −3 Ω m at 300 °C for Bi 1.99 Ni 0.01 S 3 sample. The presence of porous structures gives a significant effect on reduction of thermal conductivity, by a reduction of ~ 59.6% compared to a high density Bi 2 S 3 . The thermal conductivity of Bi 2−x Ni x S 3 ranges from 0.31 to 0.52 W/m K in the temperature range of 27 °C (RT) to 300 °C with the lowest κ values of Bi 2 S 3 compared to the previous works. A maximum ZT value of 0.13 at 300 °C was achieved for Bi 1.99 Ni 0.01 S 3 sample, which is about 2.6 times higher than (0.05) of Bi 2 S 3 sample. This work show an optimization pathway to improve thermoelectric performance of Bi 2 S 3 through Ni doping and introduction of porosity. Graphical Abstract