In y Co4Sb12 Skutterudite: Phase Equilibria and Crystal Structure

Phase relations were investigated for the In-Co-Sb system in the temperature range from 375A degrees C to 800A degrees C using as-cast and annealed alloys. Phase equilibria in the CoSb-InSb-(Sb) composition triangle are presented by a series of isothermal sections and solidus and liquidus surfaces, accompanied by a Schulz-Scheil reaction scheme. The indium-filled skutterudite In (y) Co4Sb12 already forms an equilibrium with liquid at 484A degrees C, which might limit high-temperature applications of In-Co-Sb-based skutterudites. The maximal solubility of indium in In (y) Co4Sb12 (y = 0.22) remains almost constant in the temperature range from 475A degrees C to 700A degrees C and corresponds to the equilibrium with CoSb2 and InSb. The solubility of indium in the skutterudite phase is reduced to y = 0.09 when it coexists in equilibrium with InSb and (Sb), and this decrease of the solubility might be responsible for the formation of InSb precipitates. Temperature-dependent x-ray single-crystal and specific heat data for In (y) Co4Sb12 were employed to determine the rattling behavior of In atoms in the skutterudite lattice.