Synthesis and high temperature transport properties of barium and indium double-filled skutterudites Ba_xln_yCo_4Sb_(12-z)

摘要

Barium and indium double-filled skutterudites Ba_xIn_yCo_4Sb_(12-z) have been synthesized by a melting method using a series of starting materials with nominal compositions Ba_(0.3-m)In_mCo_4Sb_(12) (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 Ba_xIn_yCo_4Sb_(12-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. Ba_(0.13)In_(0.14)Co_4Sb_(11.75) 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 Ba_xIn_yCo_4Sb_(12-z) is significantly low compared to single barium-filled skutterudite Ba_(0.27)Co_4Sb_(11.85) and reached a minimum for Ba_(0.13)In_(0.14)Co_4Sb_(11.75). 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 Ba_(0.13)In_(0.14)Co_4Sb_(11.75) at 850 K.