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

The effect of the nonstoichiometric compound terbium dioxide (Tb4O7) on the thermoelectric properties of tungsten trioxide (WO3) ceramics was investigated. Among the sintered ceramics, the sample doped with 0.1 mol% Tb4O7 showed the maximum grain size and density. Doping with Tb4O7 also increased the electrical conductivity (sigma) of the ceramics by about two orders of magnitude, and the sample doped with 0.1 mol% Tb4O7 showed the highest electrical conductivity. The absolute value of Seebeck coefficient (|S|) of the doped samples increased as well. Consequently, the power factor (sigma s (2)) markedly increased. The sample doped with 2.0 mol% Tb4O7 demonstrated the maximum sigma s (2) of 2.88 mu W m(-1) K-2 at 973 K, which was larger than the highest recorded sigma s (2) for WO3 ceramics (2.71 mu W m(-1) K-2 at 1,023 K). In addition, the low-doped sample (0.1 mol%) exhibited excellent thermoelectric properties.