On Intensifying Carrier Impurity Scattering to Enhance Thermoelectric Performance in Cr-Doped CeyCo4Sb12

• Published in: Advanced functional materials 2015-11, Vol.25 (42), p.6660-6670
• Main Authors: Wang, Shanyu, Yang, Jiong, Wu, Lihua, Wei, Ping, Zhang, Wenqing, Yang, Jihui
• Format: Article
• Language: English
• Subjects: charge compensation; electron entropy; ionized impurity scattering; thermoelectric
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201502782

The beneficial effect of impurity scattering on thermoelectric properties has long been disregarded even though possible improvements in power factor have been suggested by Ioffe more than a half century ago. Here it is theoretically and experimentally demonstrated that proper intensification of ionized impurity scattering to charge carriers can benefit the thermoelectric figure of merit (ZT) by increasing the Seebeck coefficient and decreasing the electronic thermal conductivity. The optimal strength of ionized impurity scattering for maximum ZT depends on the Fermi level and the density of states effective mass. Cr‐doping in CeyCo4Sb12 progressively increases the strength of ionized impurity scattering, and significantly improves the Seebeck coefficient, resulting in high power factors of 45 μW cm−1 K−2 with relatively low electrical conductivity. This effect, combined with the increased Ce‐filling fraction and thus decreased lattice thermal conductivity by charge compensation of Cr‐dopant, gives rise to a maximum ZT of 1.3 at 800 K and a large average ZT of 1.1 between 500 and 850 K, ≈30% and ≈20% enhancements as compared with those of Cr‐free sample, respectively. Furthermore, this study also reveals that carrier scattering parameter can be another fundamental degree of freedom to optimize electrical properties and improve thermal‐to‐electricity conversion efficiencies of thermoelectric materials. Introduction of ionized impurity scattering through Cr‐doping in CeyCo4Sb12 effectively filters low energy electrons and largely increases the overall electron entropy, thus appreciably increasing the Seebeck coefficient in a wide temperature range. This effect moderately improves the power factor and ZT by overcompensating the reduction in mobility and decreasing the thermal conductivity.