Microstructure and enhanced thermoelectric performance of Te–SnTe eutectic composites with self-assembled rod and lamellar morphology

The eutectic Te–SnTe composites with self-organized rod and lamellar structure were synthesized using the directional solidification technology. The experiments show that the volume fraction and shape-tunable morphology of the SnTe phase vary with the alloy compositions. The thermoelectric properties of the composites are dependent on the volume fraction of SnTe phase and exhibit obvious anisotropy in different growth directions. The composites perpendicular to the growth direction possess much larger S and lower κ_L than that in the parallel direction. High resolution transmission electron microscopy (HRTEM) results illustrate that there are a given amount of dislocations and atomic mismatch stress field around the Te–SnTe eutectic interface areas, which effectively scatter the heat-carrying phonons, leading to an ultralow lattice thermal conductivity of 0.64 Wm⁻¹K⁻¹ for Sn-80at%Te eutectic alloy. The obtained maximum figure of merit is 0.40 for Sn-90at%Te alloy which is 1.5–1.9 times higher than that of pure SnTe and Te, respectively. It demonstrates that introducing large amounts of eutectic interfaces in Te–SnTe composites is an effective way to enhance the thermoelectric performance.