Abstract
Skutterudites (CoSb3) are promising thermoelectric materials when properly doped with filler atoms. However, when filler atoms are Ga or In, there has been debate about where and how much those filler atoms can go into the skutterudites. The isothermal sections of the equilibrium phase diagram for the Ga-Co-Sb system at 923K and In-Co-Sb system at 873K are proposed using knowledge of the related binary phase diagrams and experimental data, which explains the debated solubilities of gallium and indium that both depend on Sb content. A fixed-composition skutterudite In0.27±0.01Co4Sb11.9 was determined for the Co-rich side of In-CoSb3 which is in coexistence with liquid InSb and CoSb2. Gallium and Indium are expected, from DFT calculations, to form compound defects in skutterudites. The charge-compensated compound defects in Ga-containing skutterudites make them intrinsic-like semiconductors. However, relatively higher carrier concentrations of In-containing skutterudites compared to Ga-containing skutterudites indicate the existence of not fully charge-compensated compound defects, which can also be explained by DFT calculations. The net n-type carrier concentration that naturally forms from the complex defects in In-containing skutterudites is close to the optimum for thermoelectric performance, enabling a maximum zT of 1.2 for the fixed skutterudite composition In0.27Co4Sb11.9 at 750K.