Improvement of thermoelectric properties of WO3 ceramics by NiO addition

The thermoelectric properties of tungsten trioxide (WO3) ceramics doped with nickel oxide (NiO) were investigated from 323 up to 1,023 K. The results revealed that doping WO3 with NiO could promote the grain growth and the density. There was a second phase (NiWO4) segregation at the grain boundaries in the samples containing more than 1.0 mol% NiO, which inhibited the further grain growth. The magnitude of the electrical conductivity (σ) and the absolute value of the Seebeck coefficient (|S|) depended strongly on the NiO content. As for the power factor (σS2), the 1.0 mol% sample has the maximum value of the power factor which is 0.55 μW m−1 K−2 at 1,023 K.