Synthesis and thermoelectric properties of tin-filled skutterudite, Sn_xCo₄Sb₁₂

Tin atoms were inserted into the skutterudite-type CoSb₃ host lattice under high pressure and temperature conditions. It was found that Sn atoms could be inserted into the body-centered vacant site, resulting in the formation of new filled (or partially filled) skutterudites, Sn_xCo₄Sb₁₂. The degree of insertion (x) increases with increasing applied pressure, and the vacant sites of the CoSb₃ host lattice is fully occupied by Sn atoms when the reaction is carried out at 8 GPa and at 550°C. X-ray Rietveld refinement revealed that the inserted Sn atom showed an anomalously large isotropic atomic displacement parameter, indicating a large thermal vibration amplitude at the body-centered position. The Sn-filled skutterudites exhibit n-type semiconducting behaviour indicating that Sn filling causes the formation of a donor level.