Transport properties and microstructure of indium-added cobalt-antimony-based skutterudites

Indium has attracted much attention as a beneficial addition to cobalt-antimony-based skutterudites as a result of good thermoelectric performance. In this study, as-cast In(x)Co(4)Sb(12) with x = 0.05, 0.2 were examined using x-ray diffraction analysis and scanning electron microscopy. For x = 0.2 we found, besides the skutterudite main phase, nanometer-sized regions of secondary phases distributed along the grain boundaries, which exhibit substructures. As-cast material with x 5 0.05 does not show visible precipitates. We further observed that changing one of the heat treatment parameters of In(0.2)Co(4)Sb(12) has a major effect on the microstructure and shape of the precipitates, but minor influence on the skutterudite matrix composition. Energy dispersive x-ray spectroscopy analysis by transmission electron microscopy) reveals that indium is to a large extent distributed into the skutterudite structure. Measurements of short-term sintered material confirm that the addition of indium and particularly the modification of the synthesis parameter entails to an enhanced ZT.