Enhancement of thermoelectric properties of Ce0.9Fe3.75Ni0.25Sb12 p-type skutterudite by tellurium addition

Abstract

Recently, research interests in p-type skutterudites are focused on multi-filling in the intrinsic void sites of Fe_4−xM_xSb₁₂. The four-membered antimony rings, another important structural feature of p-type skutterudites, seem to be overlooked. In this study, Te has been employed to substitute Sb in single-filled p-type Ce_0.9Fe_3.75Ni_0.25Sb₁₂ skutterudite and a systematic investigation has been carried out into the doping effect of Te on the microstructure and thermoelectric properties of this material. With an increase of Te doping, the electrical resistivity decreases due to the increase of hole concentration and the gradual decrease of mobility; while the density of state effective mass increases rapidly with the increase of hole concentration due to the intrinsic multiple bands effects, thus the Seebeck coefficient increases slightly. In addition, Te doping on Sb sites changes the valance electron balance and results in the formation of microscale γ-Ce and nanoscale CeTe₂ compound. These microscale and nanoscale precipitates work together with the atomic scale distortion of Sb₄ rings by the substitution of Te for Sb, could scatter phonons with a wide range of frequency thus result in a significant reduction of the lattice thermal conductivity. Therefore the thermoelectric performance has been enhanced greatly, and a maximum ZT value of 1.0 at 773 K was obtained for the Ce_0.9Fe_3.75Ni_0.25Sb_11.9Te_0.1 sample.