Tuning the thermoelectric properties of SrTiO3 by controlled oxygen doping

We report the thermoelectric properties (Seebeck coefficient, thermal conductivity, and electrical resistivity) of lightly doped single crystals of (001)-oriented SrTiO3 (STO). Hall effect measurements show that electron doping around 10^-5 carriers per unit cell can be achieved by vacuum annealing of the crystals under carefully controlled conditions. The steep density of states near the Fermi energy of STO at this doping level (confirmed by ab initio calculations) retains an unusually large Seebeck coefficient, in spite of an increase in the electronic conductivity by several orders of magnitude. This effect, combined with a decrease in thermal conductivity due to vacancy disorder scattering makes intrinsic doping in STO (and other materials) an alternative strategy to optimize its thermoelectric figure of merit.