Engineering MgAg alloy segregation at grain boundary for enhanced room-temperature n-type Mg3(Sb,Bi)2-based thermoelectrics
Grain boundary (GB) engineering has emerged as a promising strategy to enhance the near-room-temperature performance of Mg3(Sb,Bi)2-based thermoelectric materials, yet effective control of Mg distribution at GBs remains a significant challenge. Here, we report a novel approach to achieve targeted Mg segregation at GBs through strategic Ag incorporation in Mg3.3Sb0.5Bi1.497Te0.003. Through comprehensive microstructural characterization and first-principles calculations, we demonstrate that Ag preferentially segregates at GBs, forming Mg-rich MgAg alloy phases while maintaining limited solid solubility within the matrix. This unique GB architecture simultaneously optimizes multiple thermoelectric parameters: the Mg-rich GB regions significantly provide efficient carrier transport channels and enhance carrier mobility, while the MgAg phases and lattice disorders effectively scatter phonons without disrupting electron transport. Consequently, the optimized composition (x = 0.01) exhibits a remarkable enhancement in power factor at 300 K and maintains an average ZT of ~1.0 across 300–400 K. The material also demonstrates excellent mechanical properties and thermal stability, making it particularly suitable for near-room-temperature applications. Our findings not only establish an effective strategy for GB engineering in Mg3(Sb,Bi)2 systems but also provide valuable insights into the rational design of high-performance thermoelectric materials through interface modification.