Synthesis optimization and thermoelectric properties of In-filled and Te-S double-substituted skutterudite under high pressure

The high-pressure effect can effectively regulate the bandgap width of thermoelectric materials, thus optimizing the material properties. In this study, the high temperature and high pressure (HPHT) technique was employed to synthesize In-filled, Te/S double-substituted skutterudite-based thermoelectric materials. The effects of synthesis pressures ranging from 2.0 to 3.5 GPa on their phase structure, microstructure, and thermoelectric properties were systematically investigated. XRD and EDS analyses confirm the phase-pure synthesis of In 0.05 Co 4 Sb 11.3 Te 0.6 S 0.1 . The experimental results combined with first-principles calculations indicate that the pressure-induced bandgap widens from 0.245 eV at 2.0 GPa to 0.270 eV at 3.0 GPa, resulting in not only an exponential decay of the conductivity but also a significant increase in the absolute value of the Seebeck coefficient. The analysis based on the Callaway model demonstrates that introducing In, Te, and S elements strengthens grain boundaries, increases point defects, and enhances resonance scattering, thereby effectively reducing lattice thermal conductivity. At 773 K, the 3.0 GPa sample exhibits the lowest thermal conductivity of 1.56 Wm −1 K −1 and a maximum zT value of 1.20, representing a 40.18 % increase over that of the sample synthesized at 2.0 GPa and an 11.02 % increase over that of the Co 4 Sb 11.3 Te 0.6 S 0.1 sample. In addition, the sample synthesized at 3.5 GPa demonstrates excellent mechanical performance, exhibiting a Vickers hardness of 11.12 GPa. New strategies have been provided for the development of materials with both high thermoelectric and mechanical properties.