High-Pressure Synthesis and Thermoelectric Properties of Partially Filled Skutterudites <i>R_x</i>Co₄Sb₁₂ (<i>R</i> = In, Tb and Dy)

Abstract

Partially filled skutterudite compounds R x Co 4 Sb 12 (R = In, Tb and Dy, nominal composition 0.1 ¯x ¯1.5) were synthesized under high pressure using multi-anvil presses. The samples were analyzed by x-ray diffraction and scanning electron microscopy (SEM) with energydispersive x-ray spectrometry (EDX). The highest actual filling fraction x of In, Tb and Dy are 0.64, 0.22 and 0.15, respectively. The electron back-scatter diffraction (EBSD) result indicates that the grain size of In 0.8 Co 4 Sb 12 is 25 µm. Electrical resistivity, Seebeck coefficient, and thermal conductivity were measured between 2 K and 300 K. The maximum value of the dimensionless figure of merit ZT is 0.10 for nominal composition In 0.8 Co 4 Sb 12 at 300 K. We studied guest ion R dependence of lattice thermal conductivity ¬ L for R x Co 4 Sb 12 systematically based on a simple model for the rattling. The reduction rate of ¬ L of R x Co 4 Sb 12 can be scaled by a function of the guest free distance r GFD (the distance between R and Sb) and the atomic mass of R.