Incorporating donor doping into Mg3Sb1.5Bi0.5 to achieve n-type conductivity is one of the crucial strategies for performance enhancement. In pursuit of higher thermoelectric performance, we herein report co-doping with Te and Y to optimize the thermoelectric properties of Mg3Sb1.5Bi0.5, achieving a peak ZT exceeding 1.7 at 703 K in Y0.01Mg3.19Sb1.5Bi0.47Te0.03. Guided by first-principles calculations for compositional design, we find that Te-doping shifts the Fermi level into the conduction band, resulting in n-type semiconductor behavior, while Y-doping further shifts the Fermi level into the conduction band and reduces the bandgap, leading to enhanced thermoelectric performance with a power factor as high as >20 μW cm–1 K–2. Additionally, through detailed micro/nanostructure characterizations, we discover that Te and Y co-doping induces dense crystal and lattice defects, including local lattice distortions and strains caused by point defects, and densely distributed grain boundaries between nanocrystalline domains. These defects efficiently scatter phonons of various wavelengths, resulting in a low thermal conductivity of 0.83 W m–1 K–1 and ultimately achieving a high ZT. Furthermore, the dense lattice defects induced by co-doping can further strengthen the mechanical performance, which is crucial for its service in devices. This work provides guidance for the composition and structure design of thermoelectric materials.
Thermoelectric technology converts low-grade waste heat into electrical energy, offering an environmentally sustainable pathway for global development. N-type Mg3(Sb, Bi)2 thermoelectric materials have garnered significant attention due to their outstanding thermoelectric performance over broad temperatures (27–500 °C). However, unavoidable Mg loss and interfacial element diffusion degrade the performance and service life of thermoelectric devices, thereby limiting the application of thermoelectric technology. Here, we introduce elemental Mg into thermoelectric interfacial materials (TEiMs) to suppress harmful Mg diffusion and compensate for Mg loss within the material, achieving dual stability in Mg3(Sb, Bi)2 devices. After 30 days of aging, Mg3(Sb, Bi)2 single-arm devices maintained an outstanding power density of 0.75 W/cm2 and a remarkable conversion efficiency of 8.9%, demonstrating unprecedented stability. These findings offer design strategies for TEiMs and provide valuable references for interface engineering in diverse thermoelectric systems, thereby advancing the practical feasibility of thermoelectric energy harvesting in renewable energy and waste heat applications.
The n-type Mg3(Sb,Bi)2-based thermoelectric materials are promising candidates for medium-temperature power generation due to their low cost, nontoxicity, and high performance. However, their large-scale application in thermoelectric devices is significantly hindered by poor long-term stability, resulting from electrode interface degradation. Effective contact interfaces in thermoelectric devices require high bonding strength, low interfacial resistivity, and exceptional stability. Therefore, the development of efficient and reliable thermoelectric interface materials is crucial for the practical application of these devices. Conventional approaches to forming interfacial barrier layers mainly rely on thermodynamic equilibrium, which often overlook the critical roles of interfacial reactions and diffusion kinetics. In this study, molecular dynamics simulations were employed to uncover the underlying mechanisms responsible for the high stability of the Mg2Ni barrier layer and its interface with thermoelectric materials. The Mg2Ni/Mg3.21Sb1.5Bi0.5Y0.04 thermoelectric device exhibited excellent performance, with a low contact resistance of 11 μΩ·cm2, a high output power density of 1.2 W·cm–2, and an energy conversion efficiency of 5% at a temperature difference of ΔT = 373 K. This strategy is applicable to other thermoelectric materials, offering valuable insights for designing barrier layers in diverse thermoelectric systems.
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