Improvements in the thermoelectric efficiency of SrTiO3 through donor doping

The SrTiO3 perovskites n-doped with Sm3+, Dy3+, and Nb5+ were prepared via the conventional solid state reaction route (SSR) followed by spark plasma sintering (SPS) process. The SPS in dynamic vacuum promotes formation of Ti3+ and Nb4+ species, as verified by the XPS analysis. Presence of the reduced cations, primarily Ti3+, is in agreement with the observed color changes and enhanced electrical conductivity of the samples. The Sr-site substitution by Sm and Dy is highly effective in phonon scattering and reducing the lattice thermal conductivity. Besides, this substitution significantly increases the electron mobility and electrical conductivity, by reducing the lattice strain imposed by the Ti/Nb substitution. Thermoelectric measurements indicated that a doubly doped sample with the Sr0.95Sm0.05Ti0.9Nb0.1O3 loading chemical composition reached the figure of merit (zT) value of 0.41 at 873 K. Such a high zT value originates primarily from a high carrier mobility of 24 cm2/V s and a low thermal conductivity of 2.4 W/m K.