Effect of Nb doping on microstructures and thermoelectric properties of SrTiO3 ceramics**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403803), the National Natural Science Foundation of China (Grant Nos. 51774065, 51525401, 51690163, and 51601028), and the Dalian Support Plan for Innovation of High-level Talents (Top and Leading Talents) (Grant No. 2015R013).

Abstract

Nb-doped SrTiO3 thermoelectric ceramics with different niobium concentrations, sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering. For fully understanding the effect of niobium doping on SrTiO3, thermoelectric transport properties are systematically investigated in a temperature range from 300 K to 1100 K. The carrier mobility can be significantly enhanced, and the electrical conductivity is quadrupled, when the sintering temperature rises from 1673 K to 1773 K (beyond the eutectic temperature (1713 K) of SrTiO3–TiO2). The lattice vibration can be suppressed by the lattice distortion introduced by the doped niobium atoms. However, Sr-site vacancies compensate for the lattice distortion and increase the lattice thermal conductivity more or less. Finally, we achieve a maximum value of figure-of-merit zT of 0.21 at 1100 K for SrTi0.9Nb0.1O3 ceramic sintered at 1773 K.