LOW-TEMPERATURE TRANSPORT-PROPERTIES OF THE FILLED SKUTTERUDITES CEFE4-XCOXSB12

Thermal conductivity, thermoelectric power, electrical resistivity, Ha ll coefficient, and magnetic susceptibility of the filled skutterudite s CeFe4-xCoxSb12, with x = 0, 0.5, 1.0, 1.5, and 2.0, have been studie d from 2 to 300 K. We find that the substitution of Co at Fe sites has a dramatic effect on all transport properties. While the resistivity of CeFe4Sb12 has a metallic character, substitution of Co leads to a p rogressively stronger activated behavior and a decrease in hole concen tration. The thermopower increases with increasing Co, while the therm al conductivity is depressed, notably at low temperatures. Susceptibil ity data suggest the presence of large effective moments. At high temp eratures Ce is nearly trivalent, but valence fluctuations prevail at l ow temperatures. Strong hybridization of the Ce 4f states with the Fe 3d and pnicogen p states appears to be important in understanding the physical properties of these compounds.