Solid solution formation: improving the thermoelectric properties of skutterudites

Skutterudite semiconductors possess attractive transport properties and have a good potential for achieving high thermoelectric figures of merit, ZT. Low electrical resistivities and moderate to large Seebeck coefficients are obtained in binary skutterudite compounds such as CoSb/sub 3/. However, their thermal conductivities are too high (100 to 150 /spl times/10/sup -3/ Wcm/sup -1/K/sup -1/ at 300 K) to achieve high ZT values. It is well known that the formation of solid solutions, or alloying, can substantially reduce the lattice thermal conductivity of semiconductors. Because a large number of skutterudite compounds, solid solutions and related phases exist, these materials offer many possibilities for optimizing the thermal and electrical properties to a specific range of temperature. An overview of the formation of skutterudite solid solutions is given. It is shown that a substantial decrease of thermal conductivity can be achieved in cases where the fluctuations of atomic masses and volumes can be maximized and the possibility of achieving high ZT values is discussed.