Convergence of multi-valley bands as the electronic origin of high thermoelectric performance in CoSb3 skutterudites

• Published in: Nature materials Vol. 14; no. 12; pp. 1223 - 1228
• Main Authors: Tang, Yinglu, Gibbs, Zachary M., Agapito, Luis A., Li, Guodong, Kim, Hyun-Sik, Nardelli, Marco Buongiorno, Curtarolo, Stefano, Snyder, G. Jeffrey
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-12-2015; Nature Publishing Group
• Subjects: 119/118; 121/135; 639/301/1034; 639/301/299/2736; Biomaterials; Condensed Matter Physics; Electronics; Heat conductivity; High temperature; Materials Science; Nanotechnology; Optical and Electronic Materials; solar (photovoltaic), solar (thermal), solid state lighting, phonons, thermal conductivity, thermoelectric, defects, mechanical behavior, charge transport, spin dynamics, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly), synthesis (scalable processing); Thermal conductivity
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat4430

Filled skutterudites R
x
Co
4
Sb
12
are excellent n-type thermoelectric materials owing to their high electronic mobility and high effective mass, combined with low thermal conductivity associated with the addition of filler atoms into the void site. The favourable electronic band structure in n-type CoSb
3
is typically attributed to threefold degeneracy at the conduction band minimum accompanied by linear band behaviour at higher carrier concentrations, which is thought to be related to the increase in effective mass as the doping level increases. Using combined experimental and computational studies, we show instead that a secondary conduction band with 12 conducting carrier pockets (which converges with the primary band at high temperatures) is responsible for the extraordinary thermoelectric performance of n-type CoSb
3
skutterudites. A theoretical explanation is also provided as to why the linear (or Kane-type) band feature is not beneficial for thermoelectrics.
It is shown that the large thermoelectric capability of CoSb
3
skutterudite can be associated with a secondary conduction band with high valley degeneracy, which can converge with the light conduction band at high temperatures.