image: Schematic of the local-reaction global-diffusion concept and performances of the Mg3(Sb,Bi)2-based modules in power generation and thermoelectric cooling.
Credit: ©Science China Press
Mg3(Sb,Bi)2-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.
Recently, published on Science Bulletin, a joint team of researchers, from Institute of Physics, Chinese Academy of Sciences, Institute of Physics, RWTH Aachen University, Spallation Neutron Source Science Center China and University of Glasgow, report a novel in-situ Mg-vacancy engineering strategy in Mg3(Sb,Bi)2 where excess Mg is generated from local reactions between a selection of specific transition metals and the component anionic element(s) in Mg3(Sb,Bi)2 during spark-plasma-sintering. This process effectively refills matrix Mg-vacancies through the subsequent global diffusion of Mg cations in Mg3(Sb,Bi)2 lattices. This local-reaction-global-diffusion concept, contrasting with reported mechanisms associated with localized grain-boundary engineering, is elaborated through multiscale investigation. Vacancy-restrained Mg3(Sb,Bi)2 demonstrates remarkably enhanced carrier mobility and zTs, achieving record-high power factors. The fabricated Mg3Sb0.5Bi1.5/MgAgSb and Mg3SbBi/MgAgSb modules achieve record-high dual-output performance with power-density/efficiency values of 1.23 W cm−2/11.7% and 1.05 W cm−2/12.8%, respectively, under a temperature difference (ΔT) of 315 K. The constructed Mg3Sb0.5Bi1.5/Bi0.5Sb1.5Te3 and Mg3Sb0.75Bi1.25/Bi0.5Sb1.5Te3 Peltier modules deliver competitive cooling ΔTmax exceeding 70 and 67 K, respectively, at 303 K. This 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.
The authors acknowledge funding from the National Key Research and Development Program of China (2022YFB3803900), the granted beam time on the General Purpose Powder Diffractometer (https:/cstr.cn/31113.02.CSNS.GPPD) from the China Spallation Neutron Source, and support from the Research Platform of Material Genome and the Synergic Extreme Condition User Facility in Huairou, Beijing, China.