Electron sandwich doubles the thermoelectric power factor of SrTiO${}_3$

Thermoelectric materials convert a temperature difference into electricity through a phenomenon known as the Seebeck effect, and their efficiency is determined by the dimensionless figure of merit, ZT (≡ S${}^2$ · σ · κ${}^{-1}$). Currently, most materials exhibiting high ZT values (ZT > 1) are based on heavy metal compounds, but these materials have low thermal/chemical stability. In this regard, conducting metal oxides attract much attention for thermoelectric power generations at high temperatures based on their advantages in thermal stability over heavy metal compounds. However, the thermoelectric performance of metal oxides is usually low. Here the authors review that an enhanced two‐dimensionality is efficient for enhancing the thermoelectric power factor of metal oxides. The authors fabricate SrTiO${}_3$‐based superlattices of [N unit cell SrTi${}_{1-x}$Nb${}_x$O${}_3$|11 unit cell SrTiO${}_3$]${}_{10}$, of which the de Broglie wavelengths can be tuned by the substitution of Nb. The maximum power factor of the superlattice composed of the long de Broglie wavelength SrTi${}_{1-x}$Nb${}_x$O${}_3$ exceeds ≈5 mW m${}^{-1}$ K${}^{-2}$, which doubles the value observed from the optimized bulk SrTi${}_{1-x}$Nb${}_x$O${}_3$. This finding can help to reduce the amount of wasted heat and thus wasted fossil fuel in daily activities and industrial factories. (© 2019 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)