Investigation of the thermoelectric properties of Nb and oxygen vacancy co-doped SrTiO3 ceramics

High quality Nb doped SrTi1-xNbxO3 polycrystalline ceramics were fabricated using a conventional solid state reaction method. By annealing in a reducing atmosphere at an elevated temperature, a series of Nb and oxygen vacancy co-doped SrTi1-xNbxO3-delta (0 <= x <= 0.2) samples was obtained. The thermoelectric properties of the samples were measured in the temperature range from 15 K to 380 K. These measurements showed that the transport behavior of these samples is consistent with the small polaron conduction mechanism for the temperature range from room temperature to 380 K. Furthermore, after annealing, samples with a lower Nb doping were found to give a relative higher ZT value, while excess Nb led to a reduced ZT value. The x = 0.02 sample gave the optimal thermoelectric properties, with a ZT value of 0.023 at 300 K, and 0.028 at 380 K.