Thermo-Electro-Magnetic Interactions and ≈1 nm Fe Interfacial Layer Realize High Average ZT in Fe/Mg3(Sb,Bi)2 Below 300 °C

Mg 3 (Sb,Bi) 2 alloys offer exceptional near-room temperature thermoelectric (TE) performance comparable to Bi 2 Te 3 . However, the low carrier mobility due to Mg vacancies and relatively high lattice thermal conductivity adversely affect overall TE performance. Herein, carrier mobility and thermal conductivity of Mg 3 (Sb,Bi) 2 are decoupled by modulating both the phase interface and grain boundaries through incorporating different sizes of iron (Fe). Ferromagnetic micrometer-sized Fe particles enhance the figure of merit ( ZT ) more than superparamagnetic nano-sized counterparts. Magnetic moments of Fe induce the charge density overlap near phase boundaries and ≈1 nm Fe interfacial layer lowers grain-boundary barriers, leading to sharply increased carrier mobility. Moreover, the additional magnon-phonon scattering reduces lattice thermal conductivity by over 40%. Consequently, Fe/Mg 3 (Sb,Bi) 2 composite achieves a high average ZT of 1.4 over room temperature to 573 K. The fabricated Mg 3 (Sb,Bi) 2 -CdSb module demonstrates a high conversion efficiency of 8.4% under a 275 K temperature gradient, among the best for Mg 3 (Sb,Bi) 2 -based modules. This work uncovers the role of thermo-electro-magnetic interactions in bolstering TE performance and inspires the development of low-cost, high-efficiency TE modules for low-grade heat recovery.