Solid solubility of Ir and Rh at the Co sites of skutterudites

Phase diagrams for skutterudite solid solutions made by alloying at the Co site of $\mathrm{Co}{\mathrm{Sb}}_3$ skutterudite structure are studied by density functional theory. A limited solid solubility is observed for ${\mathrm{Ir}}_x{\mathrm{Co}}_{1-x}{\mathrm{Sb}}_3$ and ${\mathrm{Rh}}_x{\mathrm{Co}}_{1-x}{\mathrm{Sb}}_3$ , showing good agreement with experimental reports. A correlation between solubility and material preparation procedure is discussed. A simple method to synthesize skutterudite nanocomposites is proposed. Our calculations also demonstrate that ${\mathrm{Ir}}_x{\mathrm{Rh}}_{1-x}{\mathrm{Sb}}_3$ is a compound with ordered structure rather than a random solid solution.