High temperature thermoelectric properties of Nb-doped ZnO ceramics

Solid-state reaction processing technique was used to prepare Zn_xNb_1−xO (0≤x≤0.02) polycrystalline bulk samples. In the present study, we find that their lattice parameters a and c tend to decrease with increasing amount of Nb additive. The electrical conductivity of all the Zn_1−xNb_xO samples increased with increasing temperature, indicating a semiconducting behavior in the measured temperature range. The addition of Nb₂O₅ to ZnO led to an increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient. The best performance at 1000 K has been observed for nominal 0.5 at% Nb-doped ZnO, with an electrical resistivity of about 73.13 (S cm⁻¹) and Seebeck coefficient of ∼257.36 μV K⁻¹, corresponding to a power factor (S²σ) of 4.84×10⁻⁴ Wm⁻¹ K⁻². The thermal conductivity, κ, of the oxide decreased as compared to pure ZnO. The figure of merit ZT values of ZnO-doped Nb₂O₅ samples are higher than the ZnO pure sample, demonstrating that the Nb₂O₅ addition is fairly effective for enhancing thermoelectric properties.