Enhanced thermoelectric and mechanical performance of Bi2S3 bulk materials by compositing with Bi0.33(Bi6S9)Br nanorods

Recently, Bi₂S₃ has garnered significant interest in the thermoelectric field due to its abundant and low-toxicity constituents. Nevertheless, pure Bi₂S₃ material has not been utilized in thermoelectric applications because of its low electrical conductivity. This study presents the fabrication of the Bi_0.33(Bi₆S₉)Br-doped Bi₂S₃ bulk samples with high electrical conductivity and mechanical performance via the melting method in conjunction with spark plasma sintering technology. The increased electron concentration is attributed to the replacement of S²⁻ by Br⁻ and the introduction of extra Bi in the lattice. At 323 K, the electrical conductivity of the Bi₂S₃ + 3 wt% Bi_0.33(Bi₆S₉)Br sample increased to 208 Scm⁻¹, signifying a 3-order-of-magnitude enhancement compared to the pure sample. The enhanced electrical conductivity led to the optimization of the electrical transport properties. At 573 K, the Bi₂S₃ + 2 wt% Bi_0.33(Bi₆S₉)Br bulk sample achieved a peak power factor value of 481 μWm⁻¹K⁻², which is four times higher than that of the pure sample. Notably, the low lattice thermal conductivity of the Bi₂S₃ + 5 wt% Bi_0.33(Bi₆S₉)Br sample was 0.56 W⁻¹ m⁻¹K⁻¹ at 673 K. Given the significantly enhanced electrical transport properties and suppressed thermal conductivity, the Bi₂S₃ + 2 wt% Bi_0.33(Bi₆S₉)Br sample achieved a peak ZT value of 0.45 at 673 K and a high ZT_ave value of 0.33 from 373 to 673 K. Compared to the pure Bi₂S₃ sample, these values are 5 times and 3 times higher, respectively. Such advancements can be implemented in the domain of power generation. Additionally, the mechanical properties of the sample exhibited substantial enhancement, and the average hardness of the 2 wt% Bi_0.33(Bi₆S₉)Br-doped sample increased from 2.73 GPa of the pure sample to 3.03 GPa. This novel strategy of dual point defects modulation provides a new pathway to enhance the thermoelectric performance of Bi₂S₃ and other material systems.