Low thermal conductivity of SrTiO ₃ −LaTiO ₃ and SrTiO ₃ −SrNbO ₃ thermoelectric oxide solid solutions

Abstract

Abstract Electron‐doped SrTiO 3 has been attracting attention as oxide thermoelectric materials, which can convert wasted heat into electricity. The power factor of the electron‐doped SrTiO 3 , including SrTiO 3 ‐LaTiO 3 and SrTiO 3 ‐SrNbO 3 solid solutions, has been clarified. However, their thermal conductivity ( κ ) has not been clearly identified thus far. Only a high κ (>12 W m −1 K −1 ) has been assumed from the electron contribution based on Wiedemann–Franz law. Here, we show that the κ of the electron‐doped SrTiO 3 is lower than the assumed κ , and its highest ZT exceeded 0.1 at room temperature. The κ slightly decreased with the carrier concentration ( n ) when n is below 4 × 10 21 cm −3 . In the case of SrTiO 3 ‐SrNbO 3 solid solutions, an upturn in κ was observed when n exceeds 4 × 10 21 cm −3 due to the contribution of conduction electron to the κ . On the other hand, κ decreased in the case of SrTiO 3 ‐LaTiO 3 solid solutions probably due to the lattice distortion, which scatters both electrons and phonons. The highest ZT was 0.11 around n = 1 × 10 21 cm −3 . These findings would be useful for the future design of electron‐doped SrTiO 3 ‐based thermoelectric materials.