Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr_0.95Gd_0.05)TiO₃ ceramics

(Sr_0.95Gd_0.05)TiO₃ (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ～ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ～ 0.24 is achieved at ～ 1000 K for the samples sintered at 1648 K and 1748 K, which was ～ 71% larger than that (0.14 at ～ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.