Improvement of Thermoelectric Transport Properties in Nanostructured CoSb₃ through Heterovalent Bi Substitution

The effect of heterovalent bismuth (Bi) substitution at the cobalt (Co) site in CoSb 3 on its thermoelectric properties is systematically investigated. Samples of Co 1− X Bi X Sb 3 (0 ≤ x ≤ 0.08) are synthesized using the hydrothermal method. The structural, morphological, and electrical properties of the samples are analyzed using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and Hall effect measurements. The substitution of Bi in CoSb 3 leads to an increase in carrier concentration, which results in an enhanced power factor. Notably, the Co 0.94 Bi 0.06 Sb 3 sample achieves a power factor of 0.35 × 10 −4 W m −1 K − 2 at 550 K. Furthermore, the Co 0.92 Bi 0.08 Sb 3 sample demonstrates a low lattice thermal conductivity of 0.76 W m −1 K −1 at 700 K, attributed to increased phonon scattering. A figure of merit (zT) of 0.15 at 650 K is observed for Co 0.96 Bi 0.04 Sb 3 , highlighting the potential of Bi substitution in enhancing the thermoelectric properties of CoSb 3 .