Doping Effect of La and Dy on the Thermoelectric Properties of SrTiO3

To study the thermoelectric properties of SrTiO3 doped with lanthanum and dysprosium, ceramic samples were prepared using the conventional solid-state reaction method. The total doping amount was fixed at 20 mol% with different amounts of lanthanum and dysprosium contents. The X-ray diffraction pattern suggests that the main crystal structure is cubic perovskite with a small amount of the second phase of Dy2Ti2O7. Scanning electronic microscope surface morphology images revealed that the ceramic samples consisted of homogeneous grains with an average grain size of 4.1-6.2 mu m. The electrical conduction of the samples as a function of temperature had similar behavior to that of metallic conductivity. The Seebeck coefficients were negative, which indicates that electrons were the dominant carriers. As the dysprosium content increased, both the electrical conductivity and thermal conductivity decreased; in contrast, the absolute value of the Seebeck coefficient increased. The power factor reached 1318 mu W/K2m at 570 K with 12% dysprosium and 8% lanthanum doped in SrTiO3. The lowest thermal conductivity was 2.3 W/mK for the sample with 20% dysprosium as a dopant. The maximum figure of merit (ZT) of 0.36 at 1076 K was obtained for SrTiO3 doped with 12% dysprosium and 8% lanthanum, which is a result of the high power factor combined with low thermal conductivity.