Hydride Anion Substitution Boosts Thermoelectric Performance of Polycrystalline SrTiO3 via Simultaneous Realization of Reduced Thermal Conductivity and High Electronic Conductivity

The development of environmentally benign thermoelectric materials with high energy conversion efficiency (ZT) continues to be a long‐standing challenge. So far, high ZT has been achieved using heavy elements to reduce lattice thermal conductivity (κlat). However, it is not preferred to use such elements because of their environmental load and high material cost. Here a new approach utilizing hydride anion (H−) substitution to oxide ion is proposed for ZT enhancement in thermoelectric oxide SrTiO3 bulk polycrystals. Light element H− substitution largely reduces κlat from 8.2 W/(mK) of SrTiO3 to 3.5 W/(mK) for SrTiO3−xHx with x = 0.216. The mass difference effect on phonon scattering is small in the SrTiO3−xHx, while local structure distortion arising from the distributed Ti−(O,H) bond lengths strongly enhances phonon scattering. The polycrystalline SrTiO3−xHx shows high electronic conductivity comparable to La‐doped SrTiO3 single crystal because the H− substitution does not form a grain boundary potential barrier and thus suppresses electron scattering. As a consequence, SrTiO3−xHx bulk exhibits maximum ZT = 0.11 at room temperature and the ZT value increases continuously up to 0.22 at T = 657 K. The H− substitution idea offers a new approach for ZT enhancement in thermoelectric materials without utilizing heavy elements. A new approach by hydride anion (H–) substitution is proposed for thermoelectric performance (ZT) enhancement in environment‐friendly SrTiO3 bulk polycrystals without using heavy elements. The H− substitution reduces lattice thermal conductivity by enhanced phonon scattering while it keeps high electronic conductivity comparable to La‐SrTiO3 single crystal, resulting in ZT = 0.11 at room temperature.