Simultaneous Realization of Single-Crystal-Like Electron Transport and Strong Phonon Scattering in Polycrystalline SrTiO_3–xH_x

Simultaneous realization of low thermal conductivity (κ) and high electronic conductivity (σ) has been a challenging issue in developing high-performance thermoelectric bulk materials. SrTiO 3 has been expected as an environmentally benign thermoelectric material, but the intrinsically high κ and low σ across the grain boundaries (GBs) restrict their performance. We recently tackled this obstacle by applying hydride anion (H – ) substitution, namely, SrTiO 3– x H x . In this paper, in order to clarify the H – substitution effect on electron and phonon scattering, we analyzed the temperature dependence of electronic and thermal transport properties of the SrTiO 3– x H x bulks with different H – concentrations x = 0.057–0.216. The carrier mobility was dominated by electron–electron scattering and impurity scattering; however, the GBs did not disturb the electron transport, and thus, the high σ approaching to 10 4 S/cm at 4 K was realized in SrTiO 3– x H x bulks. The H – substitution concurrently suppressed the κ from 9.7 W/(mK) of SrTiO 3 to 5.0 W/(mK) of the SrTiO 3– x H x bulk with x = 0.216 at room temperature. The phonon scattering by elastic strain field due to the largely different chemical bonding state of Ti-(O,H) bonds is found to be prominent for reducing κ. The H – substitution approach would provide a possibility for developing environmentally benign thermoelectric oxides by the simultaneous realization of single-crystal-like electron transport and strong phonon scattering.