High temperature thermoelectric properties of Nb-doped ZnO ceramics

• Solid-state processing reaction technique was used to prepare ZnxNb1−xO bulk samples.
• The transport and thermoelectric properties for all samples were investigated.
• The intrinsic acceptors like the zinc vacancy can trap electrons.
• The Nb2O5 addition is fairly effective for enhancing thermoelectric properties.

Solid-state reaction processing technique was used to prepare ZnxNb1−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 Zn1−xNbxO 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.