LOW-TEMPERATURE TRANSPORT-PROPERTIES OF THE FILLED AND UNFILLED IRSB3SKUTTERUDITE SYSTEM

We have measured the electrical resistivity, rho, thermoelectric power , alpha, and thermal conductivity, kappa, of the skutterudite material IrSb3 in a temperature range from 300 down to 4 K. It is found that t he electrical resistivity and thermopower decrease monotonically as th e temperature is reduced to 50-60 K. Below approximately 60 K the resi stivity rises in a semiconducting manner. It appears the thermopower e xhibits a large phonon drag peak at around 20 K and then falls towards zero. The thermal conductivity increases rapidly as the temperature i s decreased with a maximum at around 20 K, corresponding to the peak i n the thermopower. We will discuss these results and compare them to h igher temperature data from G. A. Slack and V. G. Tsoukala [(lrSb3) J. Appl. Phys. 76, 1635 (1994)]. We have also measured some of the so-ca lled ''filled skutterudites,'' Ir4LaGe3Sb9, Ir4NdGe3Sb9 and Ir(4)SaGe( 3)Sb(9). The thermoelectric properties of these materials are consider ably different than those of the unfilled sample. The thermopower is c onsiderably lower and the resistivity is a factor of 2-4 times higher than the unfilled sample at room temperature. The thermal conductivity is markedly reduced by the filling, as much as a factor of 20 reducti on for some of the systems. (C) 1996 American Institute of Physics.