Oxide thermoelectrics: redox tuning of the functional properties

Since most of the energy (~60-70 %) used in the world is discharged as waste heat, the “green” thermoelectric conversion has received a considerable attention due to its intrinsic simplicity, employing no moving parts, silent operation and excellent scalability and reliability. Driven by a need to develop low-cost and thermally stable materials for thermoelectric applications, oxides are considered as a promising alternative to traditional thermoelectrics. Compared to those, oxide materials possess a unique redox flexibility and defect chemistry, which can be precisely set-up by controlled heat treatment combined with oxygen partial pressure changes. This work demonstrates how, by redox-sensitive substitutions, the thermoelectric properties of oxides can be tuned and enhanced. The developed strategies are exemplified by considering tungsten- and molybdenum- cosubstituted strontium titanate, prepared under strongly-reducing conditions. In-situ formation of nanocomposite and atomic-scale inhomogeneities composed of SrMoO3- based insertions into SrTiO3 perovskite lattice promote simultaneous significant increase in the power factor and decrease in the thermal conductivity by decoupling the thermal and electrical properties. The proposed approaches show good prospects for tailoring thermoelectric performance in other oxide-based systems, containing redox-active cations.This work was supported by UID/CTM/50011/2019 and POCI-01-0145-FEDER-031875 projects, financed by COMPETE 2020 Program and National Funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement.publishe