Enhancing the thermoelectric power factor of nanostructured ZnCo(2)O(4) by Bi substitution

Bi(x)ZnCo(2−x)O(4) (0 ≤ x ≤ 0.2) nanoparticles with different x values have been prepared by the sol–gel method; the structural, morphological, thermal and thermoelectric properties of the prepared nanomaterials are investigated. XRD analysis confirms that Bi is completely dissolved in the ZnCo(2)O(4) lattice till the x values of ≤0.1 and the secondary phase of Bi(2)O(3) is formed at higher x value (x > 0.1). The synthesized nanomaterials are densified and the thermoelectric properties are studied as a function of temperature. The electrical resistivity of the Bi(x)ZnCo(2−x)O(4) decreased with x value and it fell to 4 × 10(−2) Ω m for the sample with x value ≤ 0.1. The Seebeck coefficient value increased with the increase of Bi substitution till the x value of 0.1 and decreased for the sample with higher Bi content (x ≤ 0.2) as the resistivity of the sample increased due to secondary phase formation. With the optimum Seebeck coefficient and electrical resistivity, Bi(0.1)ZnCo(1.9)O(4) shows the high-power factor (α(2)σ(550 K)) of 2.3 μW K(−2) m(−1) and figure of merit of 9.5 × 10(−4) at 668 K respectively, compared with other samples. The experimental results reveal that Bi substitution at the Co site is a promising approach to improve the thermoelectric properties of ZnCo(2)O(4).