Thermoelectric properties of Nb-doped TiO2- ceramics reduced at elevated temperature

Abstract A series of Nb-doped TiO2-δ (Ti1-xNbxO2-δ) ceramics was fabricated using a traditional solid state reaction method with subsequent annealing in a reducing H2 atmosphere at 1573 K. From X-ray diffraction patterns it could be seen that, when x ≤ 0.04, samples were composed of mixed anorthic phases; tetragonal phase diffraction peaks for rutile TiO2 occurred in the samples with x = 0.08 and 0.20; for x = 0.40 and 0.60, only the rutile structure was seen, which suggests that the rutile structure could be maintained up to a temperature of 1573 K with a higher Nb doping level. The thermoelectric properties of the Ti1-xNbxO2-δ samples were measured in the 100–380 K temperature range. The resistivity values indicated that these samples exhibited semiconductor behavior, while their electrical transport behavior in the temperature range from room temperature to 380 K was consistent with small polaron conduction. The thermal conductivity for this series of samples gradually increased with an increase in temperature and was dominated by lattice thermal conductivity. The largest observed figure of merit ZT value, 0.016, was obtained for the sample with x = 0.20 at the highest test temperature of 380 K.