Effect of La2O3 on high-temperature thermoelectric properties of WO3

•The grain size and porosity become smaller with the increasing La2O3 content.•Increasing temperature will increase the electrical conductivity.•Increasing temperature will increase the Seebeck coefficient.•Increasing temperature will increase the power factor.•For WO3-based ceramics, the La2O3-doped WO3 has largest power factor by now.

The La2O3-added WO3 was prepared by a conventional mixed oxide processing route and the thermoelectric properties were studied from 323 K up to 1023 K. The results revealed that doping WO3 with La2O3 could promote the grain size and the density. The addition of a small amount of La2O3 (x ⩽ 0.5 mol%) to WO3 led to an marked increase in the electrical conductivity, resulting in a significant increase in the power factor. In addition, there was a second phase (La2WO6) segregation at the grain boundaries in the samples containing more than 5.0 mol% La2O3, which inhibited the further grain growth and reduced the electrical conductivity (σ) and the Seebeck coefficient (|S|). The thermoelectric power factor was maximized to a value of 3.35 μW m−1 K−2 at 1023 K for 0.5 mol% La2O3-doped WO3 sample.