Effect of Spark Plasma Sintering (SPS) on the thermoelectric properties of SrTiO3:15 at% Nb

Recently Nb doped SrTiO3 has been reported as one of the most promising n-type thermoelectric materials. In this report SrTiO3: 15 at% Nb ceramics were synthesized by Spark Plasma Sintering (SPS) route, which is a fast sintering process. Effect of sintering temperature, pressure and atmosphere on the thermoelectric power factor of STN ceramics were investigated in the present work in order to optimize the sintering condition using SPS. It was observed that STN samples sintered at 1673 K using 30 MPa pressure in Ar-atmosphere showed best thermoelectric power factor. Room temperature XRD results verified STN as a single phase solid solution with cubic crystal structure. Microstructure of these ceramics were studied using FESEM where the results confirmed the formation of sub micron range grains as expected in SPS. All the STN samples behaved as n-type semiconductor throughout the measurement. The conduction mechanism of these ceramic samples were studied using the Variable Range Hopping (VRH) and Small Polaron Hopping (SPH) model.