Predication of an ultrahigh filling fraction for K in CoSb3

Abstract

The filling fraction limit (FFL) for potassium in skutterudite $\mathrm{Co}{\mathrm{Sb}}_3$ has been investigated by first-principles methods. The FFL is derived by minimizing the formation energy of a reaction that includes the formation of both the filled skutterudite ${\mathrm{K}}_y{\mathrm{Co}}_4{\mathrm{Sb}}_{12}$ and the potential secondary phases KSb and $\mathrm{Co}{\mathrm{Sb}}_2$ when doping K into $\mathrm{Co}{\mathrm{Sb}}_3$ . Our calculations show that K has an ultrahigh filling fraction up to more than 60% in $\mathrm{Co}{\mathrm{Sb}}_3$ , as compared with those of previously reported fillers such as Sr, Ba, Ca, La, Ce, Eu, and Yb [X. Shi et al., Phys. Rev. Lett. 95, 185503 (2005)]. The extent to which this affects the thermoelectric properties of K-filled skutterudites is discussed.