Theoretical Study of the Filling Fraction Limit of Fe-Substituted Ba-Filled Skutterudite BayFe4xCo4-4xSb12

Theoretical study of the filling fraction limit (FFL) of the Fe-substituted Ba-filled skutterudite was carried out via first principle method calculations. The lattice constant of BayFe4xCo4-4xSb12 increases with the Ba filling fraction under fixed Fe content while it does not simply increases with Fe content under fixed Ba filling fraction. The FFL is determined by the competition between the formation of filled skutterudite phases and the corresponding secondary phases. The FFL of Ba in the Fe-substituted CoSb3 skutterudites increases monotonically from 37.5% with Fe content of 0 to 100% with Fe content of similar to 50%. The most stable composition of the BayFe4xCo4-4xSb12 is expected to be BaFe(2.8)Co(1.2)Sbi(12).