High performance (ZT>1) n-type oxide thermoelectric composites from earth abundant materials

Oxide-based thermoelectric materials have the advantages of high-temperature stability, low toxicity and low processing cost comparted to other metal-based systems. However, achieving ZT > 1 remain elusive especially for n-type bulk oxide thermoelectrics. Here, we report the experimental demonstration of ZT > 1 in n-type oxides by synthesizing composites of Nb-doped SrTiO3 (STN) with natural graphite. Introduction of conductive graphite inclusions in STN matrix has led to a surge in electrical conductivity due to 21-times increase in weighted mobility (mu(w)) of electrons resulting in high thermoelectric power factor similar to 5400 mu W/mK(2), which is similar to 16-times higher than that of pure STN. Furthermore, we could restrain the increase in thermal conductivity by attaining enhanced Umklapp scattering along with phonon-glass-like temperature-independent phonon mean-free-path above Debye temperature. We have achieved the maximum ZT similar to 1.42 in STN+ 0.5 wt% G composite, which is 15-times enhancement compared to STN. Our proposed way of designing rare-earth-free composites with graphite can potentially open up the possibility of fabricating novel high-temperature thermoelectric generators.