Influence of substituting Sn for Sb on the thermoelectric transport properties of CoSb3-based skutterudites

Abstract

Band structure calculations that incorporate impurity effects suggest that a band resonant state may be formed in p-type CoSb3-based skutterudites by replacing Sb atoms with Sn dopant atoms. Such resonant states have the potential to greatly improve thermoelectric energy conversion efficiency by increasing the density of states variation near the Fermi level, thereby increasing the Seebeck coefficient at a given carrier concentration. Through transport measurements of the Seebeck coefficient, electrical conductivity, thermal conductivity, and Hall coefficient, we show that a practical band resonant state is not achieved by Sn doping. Compared to undoped CoSb3, the dimensionless figure of merit (ZT) in Sn-doped CoSb3 is enhanced slightly at high temperatures to a value of 0.2, mostly due to a reduction in thermal conductivity. The Fermi level is calculated not to reach the band resonant state induced by Sn impurity atoms within the range of Sn concentrations examined here.