Improvement of thermoelectric properties of WO3 ceramics by ZnO addition

Highlights: ► Doping WO3 with ZnO can promote the grain growth and the densification. ► The addition of ZnO into WO3 raises the electrical conductivity by about two orders of magnitude. ► There exists an optimum doping concentration of ZnO in WO3 for obtaining the best power factor. ► The power factor of the sample is at least ten times larger than the data in our last paper. ► The thermoelectric properties of WO3 are greatly enhanced by the addition of ZnO. - Abstract: The thermoelectric properties of tungsten trioxide (WO3) ceramics doped with zinc oxide (ZnO) were investigated from 473 to 973 K. The results revealed that doping WO3 with ZnO could promote the grain growth and the densification. Moreover, the addition of ZnO into WO3 obviously raised the electrical conductivity (σ) of the ceramics by about two orders of magnitude with only slightly decreasing its absolute value of the Seebeck coefficient (|s|). Thus, the magnitude of the power factor (σs2) was enhanced tremendously by adding ZnO. In addition, there was a second phase (ZnWO4) segregation at the grain boundaries in the samples containing more than 0.5 mol% ZnO, which inhibited the further grain growth and reduced the σ and |s|. Therefore, there existed an optimum doping concentration of ZnO in WO3 for obtaining a better power factor.