We study the origin of the large Seebeck coefficient despite the metallic conductivity in the La-doped ${\text{SrTiO}}_3$ and Ba-doped ${\text{KTaO}}_3$. We calculate the band structure of ${\text{SrTiO}}_3$ and ${\text{KTaO}}_3$, from which the Seebeck coefficient is obtained using the Boltzmann’s equation. We conclude that the multiplicity of the $t_{2g}$ bands in these materials is one major origin of the good thermoelectric property in that when compared at a fixed total number of doped electrons, the Seebeck coefficient and thus the power factor are larger in multiple band systems than in single band ones because the number of doped electron bands per band is smaller in the former. We also find that the second-nearest-neighbor hopping integral, which generally has negative values in these materials and works destructively against the Seebeck effect, is nearly similar between ${\text{KTaO}}_3$ and ${\text{SrTiO}}_3$ despite the larger bandwidth in the former. This can be another factor favorable for thermopower in the Ba-doped ${\text{KTaO}}_3$.

• Received 1 February 2010

DOI:https://doi.org/10.1103/PhysRevB.81.205121