Microstructure and thermoelectric properties of tungsten trioxide ceramics doped with a low amount of terbium dioxide

The effect of the nonstoichiometric compound terbium dioxide (Tb 4 O 7 ) on the thermoelectric properties of tungsten trioxide (WO 3 ) ceramics was investigated. Among the sintered ceramics, the sample doped with 0.1 mol% Tb 4 O 7 showed the maximum grain size and density. Doping with Tb 4 O 7 also increased the electrical conductivity ( σ ) of the ceramics by about two orders of magnitude, and the sample doped with 0.1 mol% Tb 4 O 7 showed the highest electrical conductivity. The absolute value of Seebeck coefficient (| S |) of the doped samples increased as well. Consequently, the power factor ( σs 2 ) markedly increased. The sample doped with 2.0 mol% Tb 4 O 7 demonstrated the maximum σs 2 of 2.88 μW m −1 K −2 at 973 K, which was larger than the highest recorded σs 2 for WO 3 ceramics (2.71 μW m −1 K −2 at 1,023 K). In addition, the low-doped sample (0.1 mol%) exhibited excellent thermoelectric properties.