Local reaction-global diffusion unlocks high-performance Mg(3)(Sb,Bi)(2)-based thermoelectrics.

Mg(Sb,Bi)-based thermoelectrics (TEs) show promise for near-room-temperature energy conversion and TE-cooling applications. However, further improvements in electrical power factors and figure-of-merits (zTs) are constrained by precise Mg-vacancy regulation and elucidation of underlying mechanisms. Herein, we report a novel in-situ Mg-vacancy engineering strategy in Mg(Sb,Bi) where excess Mg is generated from local reactions between a selection of specific transition metals and the component anionic element(s) in Mg(Sb,Bi) during spark-plasma-sintering. This process effectively refills matrix Mg-vacancies through the subsequent global diffusion of Mg cations in Mg(Sb,Bi) lattices. This local-reaction-global-diffusion concept, contrasting with reported mechanisms associated with localized grain-boundary engineering, is elaborated through multiscale investigation. Vacancy-restrained Mg(Sb,Bi) demonstrates remarkably enhanced carrier mobility and zTs, achieving record-high power factors. Our fabricated MgSbBi/MgAgSb and MgSbBi/MgAgSb modules achieve record-high dual-output performance with power-density/efficiency values of 1.23 W cm/11.7% and 1.05 W cm/12.8%, respectively, under a temperature difference (ΔT) of 315 K. The constructed MgSbBi/BiSbTe and MgSbBi/BiSbTe Peltier modules deliver competitive cooling ΔT exceeding 70 and 67 K, respectively, at 303 K. The concept is expected to extend to the defect engineering of other energy materials (e.g., SnTe and PbSe TEs), TE-interface materials, and metal-semiconductor interfaces with optimized functionalities.