Enhancing the thermoelectric properties of Nb-doped TiO2-based ceramics through in-situ synthesis of β-Sn inclusions at grain boundaries

Significantly enhanced thermoelectric performance of Nb-doped TiO₂ ceramics has been achieved through in-situ formation of β-Sn grain boundary inclusions. The ceramics were prepared by mixed oxide route and sintered at 1473 K (lower than usual for TiO₂) and strongly reducing conditions. All sample microstructures contain a high density of β-Sn structured inclusions at grain boundaries which assist densification. A variety of crystalline defects occur inside the rutile grains; the β-Sn inclusions contain nano-regions with severe lattice distortion. Through the formation of a highly conductive β-Sn phase, the carrier concentration and electrical conductivity were significantly enhanced, resulting in a ～27% increase in power factor and much-improved ZT values of 0.20 at 873 K. Our approach based on grain boundary engineering provides a simple and eco-friendly route to enhance the thermoelectric performance of low-cost, oxide-based ceramics.