High-Pressure Synthesis of Te–Ge Double-Substituted\nSkutterudite with Enhanced Thermoelectric Properties

We synthesized Co<sub>4</sub>Sb<sub>11</sub>Te<sub><i>x</i></sub>Ge<sub>1–<i>x</i></sub> (<i>x</i> = 0.5–0.8) using high-pressure, high-temperature\nconditions\nat ∼2 GPa and ∼900 K. The microstructure, morphology,\nand components were characterized via X-ray diffraction, scanning\nelectron microscopy, and electron backscatter diffraction (EBSD).\nEBSD indicated that the average grain size of Co<sub>4</sub>Sb<sub>11</sub>Te<sub>0.8</sub>Ge<sub>0.2</sub> was 1 μm. Electrical\nconductivity, Seebeck coefficient, and thermal conductivity were measured\nfrom 300 to 800 K. The minimum lattice thermal conductivity of Co<sub>4</sub>Sb<sub>11</sub>Te<sub>0.8</sub>Ge<sub>0.2</sub> was 0.72 W\nm<sup>–1</sup> K<sup>–1</sup>, 74% lower than that at\n300 K. The introduction of Te and Ge effectively enhanced point effects\nscattering and location scattering, notably decreasing lattice thermal\nconductivity. Therefore, the maximum <i>zT</i> value of\nCo<sub>4</sub>Sb<sub>11</sub>Te<sub>0.8</sub>Ge<sub>0.2</sub> was\n1.13 at 800 K. These results indicate that high pressure combined\nwith multielement substitution optimized the thermoelectric transport\nproperties of skutterudites.