High-Pressure Synthesis of Te-Ge Double-Substituted Skutterudite with Enhanced Thermoelectric Properties

We synthesized Co₄Sb₁₁TeGe_1- (x = 0.5-0.8) using high-pressure, high-temperature conditions at ∼2 GPa and ∼900 K. The microstructure, morphology, and components were characterized via X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction (EBSD). EBSD indicated that the average grain size of Co₄Sb₁₁Te_0.8Ge_0.2 was 1 μm. Electrical conductivity, Seebeck coefficient, and thermal conductivity were measured from 300 to 800 K. The minimum lattice thermal conductivity of Co₄Sb₁₁Te_0.8Ge_0.2 was 0.72 W m^-1 K^-1, 74% lower than that at 300 K. The introduction of Te and Ge effectively enhanced point effects scattering and location scattering, notably decreasing lattice thermal conductivity. Therefore, the maximum zT value of Co₄Sb₁₁Te_0.8Ge_0.2 was 1.13 at 800 K. These results indicate that high pressure combined with multielement substitution optimized the thermoelectric transport properties of skutterudites.