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

Abstract

Achieving high thermoelectric efficiency across 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 a strain-mediated reconstruction of the grainboundary spectrum in Mg3Sb2-based system. The boundary-spectrum reconfiguration markedly weakens grain-boundary potential barriers and alleviates carrier scattering by raising the fraction of coherent twin boundaries, restoring the power factor near room temperature. Within the same processing window, the multifunctional CuGaTe2 additive also undergoes composition-partitioning, yielding 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, that exceeds state-of-the-art n-type Bi 2 Te 3 , while maintaining ZT ave =1.59 from 300-723 K with a peak ZT of 2.08 at 623 K. Device demonstrations further validate the materials-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 establish grain-boundary spectrum reconstruction as an effective lever to unlock high near-room-temperature performance and bridge the long-standing temperature range issue in n-type Mg3Sb2 for wideranging waste-heat recovery.