Synergistic Combination of Sb₂Si₂Te₆ Additives for Enhanced Average ZT and Single-Leg Device Efficiency of Bi_0.4Sb_1.6Te₃-based Composites

Thermoelectric materials are highly promising for waste heat harvesting. Although thermoelectric materials research has expanded over the years, bismuth telluride-based alloys are still the best for near-room-temperature applications. In this work, a ≈38% enhancement of the average ZT (300−473 K) to 1.21 is achieved by mixing Bi_0.4Sb_1.6Te₃ with an emerging thermoelectric material Sb₂Si₂Te₆, which is significantly higher than that of most Bi_ySb_2−yTe₃-based composites. This enhancement is facilitated by the unique interface region between the Bi_0.4Sb_1.6Te₃ matrix and Sb₂Si₂Te₆-based precipitates with an orderly atomic arrangement, which promotes the transport of charge carriers with minimal scattering, overcoming a common factor that is limiting ZT enhancement in such composites. At the same time, high-density dislocations in the same region can effectively scatter the phonons, decoupling the electron-phonon transport. This results in a ≈56% enhancement of the thermoelectric quality factor at 373 K, from 0.41 for the pristine sample to 0.64 for the composite sample. A single-leg device is fabricated with a high efficiency of 5.4% at ΔT = 164 K further demonstrating the efficacy of the Sb₂Si₂Te₆ compositing strategy and the importance of the precipitate-matrix interface microstructure in improving the performance of materials for relatively low-temperature applications.