Defect-Energy-Targeted Lattice Repair Delivers High Thermoelectric Performance in Magnesium Antimonide

High Resolution Image Download MS PowerPoint Slide Magnesium-based Mg 3 (Sb,Bi) 2 has emerged as a premier candidate for waste-heat recovery. However, its performance is fundamentally capped by intrinsic Mg vacancies that severely scatter carriers. Here, we overcome this bottleneck via a defect-energy-targeted lattice repair strategy, substituting labile Mg sites with homologous alkaline-earth metals (Ca, Sr, Ba). Theoretical calculations reveal that the lower electronegativity of these dopants strengthens the local metal–Sb bonding, drastically raising the vacancy formation energy from ∼0.97 to ∼2.42 eV. This thermodynamic stabilization effectively “repairs” the lattice, suppressing vacancy generation and yielding a ∼35% boost in carrier mobility without compromising carrier concentration. Simultaneously, the heavy dopants induce mass fluctuations and strain fields that, coupled with dense dislocations, minimize the lattice thermal conductivity to ∼0.4 W m –1 K –1 at 773 K. The synergy of restored charge transport and suppressed heat propagation leads to a record-high figure of merit ( zT ) of ∼2.1 at 773 K and an outstanding average zT of ∼1.5 in Mg 3.2 Ba 0.005 Sb 1.5 Bi 0.49 Te 0.01 . Remarkably, a single-leg device demonstrates a conversion efficiency of ∼14%, outperforming state-of-the-art n-type thermoelectrics. This work demonstrates that targeting defect energetics is a powerful, broadly applicable approach to breaking the performance ceilings of Zintl-phase thermoelectrics.