Realization of high thermoelectric performance in p-type unfilled ternary skutterudites FeSb2+xTe1-x via band structure modification and significant electron-phonon scattering
Gangjian Tan, Xianli Su, Wei Liu, Hang Chi, Yonggao Yan, Xinfeng Tang, Ctirad Uher, Winnie K. Wong-Ng
FeSb2Te, a ternary system derived from binary CoSb3, displays anomalous electrical and thermal transport properties because of the considerable modification in band structure induced by Fe and the significant mixed valence states (namely Fe2+ and Fe3+) scattering on phonons, showing a great potential in thermoelectric power generation. The substitution of Te by Sb generates more holes without obviously affecting the band structure, markedly improving the electrical conductivity while retaining a high Seebeck coefficient due to the enhanced density of states, thereby leading to dramatically increased power factors. Furthermore, the large effective mass coupled with the high hole density gives rise to a strong electron-phonon scattering in the FeSb2+xTe1-x compounds, which should be largely responsible for the further reduction of lattice thermal conductivity with increasing Te content (hole concentration). Consequently, high thermoelectric figures of merit were achieved in the FeSb2+xTe1-x compounds, with the largest ZT value reaching 0.65 for the sample with x=0.2, which is the highest value among all the p-type unfilled skutterudites and can be comparable with some filled compositions. Prospects for further improving the performance of p-type FeSb2Te-based skutterudites are also discussed.