The effect of rare-earth filling on the lattice thermal conductivity of skutterudites

Abstract

Polycrystalline samples of Ir₄LaGe₃Sb₉, Ir₄NdGe₃Sb₉, and Ir₄SmGe₃Sb₉ have been made by hot isostatic pressing of powders. The lattice thermal conductivity of these filled skutterudites is markedly smaller than that of IrSb₃; thus, void filling shows promise as a method for improving the thermoelectric properties of these materials. We present the lattice thermal conductivity of these filled skutterudites in an effort to quantify the impact of void filling in this structure. It is believed that the atoms ‘‘rattle’’ in the voids of the structure and therefore interact with a broad spectrum of lattice phonons, reducing their mean free paths substantially below that in the ‘‘unfilled’’ skutterudites. An additional phonon scattering mechanism is caused by phonon‐stimulated transitions between the low‐lying energy levels of the 4f electron configurations in the case of Nd³⁺ and Sm³⁺. Magnetic susceptibility and Hall‐effect measurements are also presented.