Simultaneous Realization\nof Single-Crystal-Like Electron\nTransport and Strong Phonon Scattering in Polycrystalline SrTiO<sub>3–<i>x</i></sub>H<sub><i>x</i></sub>

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