Zn-substituted CoSb₂O₆ nanostructures synthesized by sol-gel method: a novel oxide material with improved thermoelectric performance

The increasing demand for sustainable energy solutions has driven significant interest in thermoelectric (TE) materials capable of converting waste heat into electricity. In the present study, we explore the effect of zinc (Zn) substitution on the thermoelectric properties of novel CoSb₂O₆ nanostructures synthesized via the sol-gel method. Structural analysis using X-ray diffraction (XRD) confirms the phase purity and hexagonal structure of the synthesized nanomaterials. In samples with increased zinc content, the formation of a secondary ZnO phase was observed. Field emission scanning electron microscopy (FESEM) reveals a nanoflower-like morphology composed of ~50 nm spherical particles. Thermogravimetric analysis (TGA) demonstrates excellent thermal stability up to 800 °C. Pelletized samples were evaluated for their thermoelectric performance over a range of temperatures. The electrical resistivity decreased with increasing Zn content, attributed to a rise in carrier concentration. The lowest resistivity was observed in the Zn₀.₁Co₀.₉SbO₆ composition, reaching a minimum value of 0.12 Ω·m. The Seebeck coefficient decreased with Zn substitution up to x = 0.1 but increased at x = 0.2, likely due to the formation of a ZnO secondary phase, which also led to an increase in resistivity. The optimized Zn₀.₁Co₀.₉SbO₆ sample exhibited the highest power factor of 1.3 μW·K⁻²·m⁻¹ at 533 K and a figure of merit (ZT) of 4 × 10⁻⁴ at the same temperature. These results highlight Zn substitution at the Co site as a promising strategy to enhance the thermoelectric performance of CoSb₂O₆-based materials.