Thermoelectric property enhancement by Cu nanoparticles in nanostructured FeSb2

We present the thermoelectric figure-of-merit (ZT) improvement in nanostructured FeSb2 by Cu nanoparticles of ∼5 nm as a modulation dopant. Because of the similar work functions between FeSb2 and Cu and the high electrical conductivity of Cu, the Kondo insulator-like electrical resistivity of FeSb2 at low temperatures was dramatically reduced. Both carrier concentration and mobility of the nanocomposites were improved over pure FeSb2 without degrading the Seebeck coefficient. Overall, an improvement of ∼90% in power factor was achieved for the optimized nanocomposite FeSb2Cu0.045. Combined with the reduced thermal conductivity by Cu/FeSb2 interfaces, ZT was improved by ∼110%. These results clearly demonstrate the potential of modulation doping to enhance the thermoelectric performance of FeSb2. A similar approach could be applied to other Kondo insulators or previously known thermoelectric materials to improve ZT.