Low thermal conductivity of SrTiO3-LaTiO3 and SrTiO3-SrNbO3 thermoelectric oxide solid solutions

Abstract

Electron-doped SrTiO3 has been attracting attention as oxide thermoelectric materials, which can convert wasted heat into electricity. The power factor of the electron-doped SrTiO3, including SrTiO3-LaTiO3 and SrTiO3-SrNbO3 solid solutions, has been clarified. However, their thermal conductivity (kappa) has not been clearly identified thus far. Only a high kappa (>12 W m(-1) K-1) has been assumed from the electron contribution based on Wiedemann-Franz law. Here, we show that the kappa of the electron-doped SrTiO3 is lower than the assumed kappa, and its highest ZT exceeded 0.1 at room temperature. The kappa slightly decreased with the carrier concentration (n) when n is below 4 x 10(21) cm(-3). In the case of SrTiO3-SrNbO3 solid solutions, an upturn in kappa was observed when n exceeds 4 x 10(21) cm(-3) due to the contribution of conduction electron to the kappa. On the other hand, kappa decreased in the case of SrTiO3-LaTiO3 solid solutions probably due to the lattice distortion, which scatters both electrons and phonons. The highest ZT was 0.11 around n = 1 x 10(21) cm(-3). These findings would be useful for the future design of electron-doped SrTiO3-based thermoelectric materials.