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.