The effect of reduced graphene oxide on microstructure and thermoelectric properties of Nb-doped A-site-deficient SrTiO3 ceramics

As promising thermoelectric materials with great stability at high temperature, SrTiO3 based ceramics have attracted much attention, albeit the thermoelectric figure of merit remains relatively low for application. To improve the thermoelectric properties, reduced graphene oxide (RGO) is successfully incorporated into Nb-doped SrTiO3 (STNO) ceramics with Sr deficiency via a hetero-aggregation strategy followed by annealing and spark plasma sintering. The addition of RGO enhances the carrier concentration via reduction effect and increases the carrier mobility probably through lowering the double Schottky barrier at grain boundaries, resulting in highly improved electrical conductivity for the composites. Moreover, RGO also stimulates the separation of Nb rich TiO2 phase, which serves as a dispersion with low thermal conductivity to prohibit the phonon transport in the composites. Consequently, a ZT value reaching 0.22 at 800 K for the RGO/STNO nanocomposite is obtained, which is 1.8 times higher compared with the monolithic STNO.