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 CoSb₃ on its thermoelectric properties is systematically investigated. Samples of Co_1-XBi_XSb₃ (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 CoSb₃ leads to an increase in carrier concentration, which results in an enhanced power factor. Notably, the Co_0.94Bi_0.06Sb₃ sample achieves a power factor of 0.35 × 10^-4 W m^-1 K^{- 2} at 550 K. Furthermore, the Co_0.92Bi_0.08Sb₃ 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_0.96Bi_0.04Sb₃, highlighting the potential of Bi substitution in enhancing the thermoelectric properties of CoSb₃.