Synthesis and high temperature transport properties of barium and indium double-filled skutterudites BaxInyCo4Sb12-z

Barium and indium double-filled skutterudites BaxInyCo4Sb12-z have been synthesized by a melting method using a series of starting materials with nominal compositions Ba0.3-mInmCo4Sb12 (0 <= m <= 0.3). Rietveld structure refinement shows that both barium and indium occupied the Sb-icosahedron voids in skutterudite structure. The thermal vibration parameter U-iso of indium is an order of magnitude bigger than that of barium. The electron probe microanalysis data prove that the filling fraction limit of indium is about 0.22. Hall effect was measured by the Van de Pauw method at room temperature. All BaxInyCo4Sb12-z compounds exhibit n-type conduction. The temperature dependences of electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured on these compounds in the range of 300-850 K. Ba0.13In0.14Co4Sb11.75 with close filling fractions for barium and indium exhibits anomalously excellent thermoelectric properties, which may be due to the presence of the localized state in the gap occupied by one electron from indium impurity. The lattice thermal conductivity of BaxInyCo4Sb12-z is significantly low compared to single barium-filled skutterudite Ba0.27Co4Sb11.85 and reached a minimum for Ba0.13In0.14Co4Sb11.75. The dimensionless thermoelectric figure of merit ZT increased with increasing temperature in the range of 300-675 K and reached a maximum value of 1.19 for Ba0.13In0.14Co4Sb11.75 at 850 K. (c) 2007 American Institute of Physics.