Structure Optimization and Multi-frequency Phonon Scattering Boosting Thermoelectrics in Self-Doped CoSb₃-Based Skutterudites

The utilization of thermoelectric devices that directly convert waste heat to electricity is an effective approach to alleviate the global energy crisis. However, the low efficiency of thermoelectric materials has puzzled the widespread applications. The CoSb₃-based skutterudites are favored by device integration due to the excellent thermal stability, while the development of pristine CoSb₃ materials is limited by the ultra-high thermal conductivity and the poor Seebeck coefficient. In this work, we demonstrate that both structural improvement and strong phonon interaction are realized simultaneously in In-filled CoSb₃ coordinated with excessive Sb. The extra Sb compensates the deficiency on the Sb₄ ring, improving the Seebeck coefficient, and cooperates with In to further advance the carrier concentration. Therefore, the structure optimization and chemical potential regulation maximize the electrical properties. Thermally, the residual InSb nanoparticles and partial In/Sb-alloying, along with vibration of In in voids, jointly shorten the multi-frequency phonon relaxation time, leading to a dramatic decline in the lattice thermal conductivity. As a result, a maximum zT_max of ∼1.27 at 650 K and an average zT_avg of ∼0.9 from 300 to 750 K was obtained in In_1.4Co₄Sb₁₂ + 8%Sb, respectively. Our findings provide valuable guidance for the selection of CoSb₃-based skutterudite dopants to achieve high-performance thermoelectric materials.