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 mu Wm(-1)K(-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(-1)K(-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.