Combined effect of donor doping and RGO (reduced graphene oxide) coating in La/Nb-doped SrTiO3 thermoelectrics

SrTiO3 (STO) is one of the most promising oxide thermoelectric (TE) materials with high thermopower, but the low electrical conductivity and high thermal conductivity are still issues to be solved. Recently, grain boundary engineering using reduced graphene oxide (RGO) has been demonstrated to have capable of simultaneously improving both the electrical and thermal properties of STO. In this study, we investigated the combined effect of La/Nb doping and RGO coating in STO to improve further the electrical conductivity and the TE efficiency of STO materials. Two series of La- and Nb-doped Sr1-xLaxTi1-yNbyO3 (x, y = 0-0.02) samples incorporated with RGO were prepared by a combinatorial procedure of solid-state reaction, RGO coating, and the spark plasma sintering (SPS) process. The structural, morphological and temperature-dependent thermoelectric properties of the Sr1-xLaxTi1-yNbyO3/RGO were studied and as a result, the figure of merit was enhanced similar to 6.5 times by the combined effect of donor doping and lowering the double Schottky barrier height due to RGO at grain boundaries.