THE EFFECT OF RARE-EARTH FILLING ON THE LATTICE THERMAL-CONDUCTIVITY OF SKUTTERUDITES

Polycrystalline samples of Ir4LaGe3Sb9,Ir4NdGe3Sb9, and Ir4SmGe3Sb9 ha ve been made by hot isostatic pressing of powders. The lattice thermal conductivity of these filled skutterudites is markedly smaller than t hat of IrSb3; thus, void filling shows promise as a method for improvi ng the thermoelectric properties of these materials. We present the la ttice thermal conductivity of these filled skutterudites in an effort to quantify the impact of void filling in this structure. It is believ ed that the atoms ''rattle'' in the voids of the structure and therefo re interact with a broad spectrum of lattice phonons, reducing their m ean free paths substantially below that in the ''unfilled'' skutterudi tes. An additional phonon scattering mechanism is caused by phonon-sti mulated transitions between the low-lying energy levels of the 4f elec tron configurations in the case of Nd3+ and Sm3+. Magnetic susceptibil ity and Hall-effect measurements are also presented. (C) 1996 American Institute of Physics.