Strain-mediated grain-boundary reconstruction unlocks high near-room-temperature thermoelectric performance in Mg3Sb2-based alloys

Abstract

Achieving high thermoelectric efficiency across a wide temperature range, including near room temperature, within a single Mg₃Sb₂-based material remains challenging, because the microstructures that favor low-temperature charge transport often conflict with those required for phonon suppression. Here, we demonstrate that subtle lattice perturbations can steer strain-mediated grain-boundary spectrum reconstruction in Mg₃Sb₂-based systems. The grain-boundary spectrum reconfiguration markedly weakens grain-boundary potential barriers and alleviates carrier scattering by raising the fraction of coherent twin boundaries, thereby restoring the power factor near room temperature. Within the same processing window, the multifunctional CuGaTe₂ additive also undergoes composition-partitioning, yielding a uniformly dispersed in situ Cu–Ga-rich intermetallic phase together with point defects. The resulting multi-length-scale defect landscape provides broadband phonon scattering and suppresses lattice thermal conductivity toward the diffusion limit. Consequently, the optimized alloy delivers an exceptional ZT_ave of 1.3 at ΔT = 250 K, exceeding that of state-of-the-art n-type Bi₂Te₃, while maintaining a ZT_ave of 1.59 from 300–723 K with a peak ZT of 2.08 at 623 K. Device demonstrations further validate the material-level advantages with 8% for the assembled TE module (ΔT = 300 K) and 12.4% for a single-leg generator (ΔT = 400 K). These results indicate that grain-boundary spectrum reconstruction can serve as an effective route to improve near-room-temperature performance and help narrow the performance gap between the near-room- and mid-temperature regimes in n-type Mg₃Sb₂ for broader waste-heat recovery.