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Abstract 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 Bi0.4Sb1.6Te3 with an emerging thermoelectric material Sb2Si2Te6, which is significantly higher than that of most BiySb2−yTe3‐based composites. This enhancement is facilitated by the unique interface region between the Bi0.4Sb1.6Te3 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.

Decades of studies on thermoelectric materials have enabled the design of high‐performance materials based on basic materials properties, such as bandgap engineering. In general, bandgap energies correspond to the temperature at which the peak thermoelectric performance occurs. For instance, CuGaTe2 with a relatively wide bandgap of 1.2 eV has its peak zT > 1 at > 900 K. On the other hand, the zT is usually very low (

In this work, we compare the thermoelectric performance of Mg _2 Si-based compounds by synthesizing them in N _2 compared to Ar atmosphere during ball milling. In addition, we achieved high thermoelectric performance by introducing Sn-alloying as well as Zn- and Bi-co doping. The high performance originated from simultaneous improvement in electrical conductivity and reduced thermal conductivity. This results in peak zT near 1.0 at 760 K for Mg _1.9925 Zn _0.0075 Si _0.48 Sn _0.5 Bi _0.02 . Owing to the much lower cost (higher abundance) of N _2 compared to Ar owing to their much higher relative abundance, such processing strategy is expected to improve sustainability. Furthermore, the insights derived from this work can potentially be applied to other compounds containing Mg- and other reactive elements. Fundamentally, this result will also motivate further studies on the intrinsic defect formation in N _2 vs Ar atmosphere, which affects both electronic and thermal transports.