Defect‐Mediated Compliance in Plasma‐Sprayed Fe─Mn Barriers Enables Durable and Efficient Bi ₂ Te ₃ Modules

ABSTRACT Interfaces, rather than bulk zT values, fundamentally govern the performance and reliability of thermoelectric modules. Taking Bi ₂ Te ₃ as a representative system, we design a plasma‐sprayed FeMn ₁₇ barrier that ensures thermal‐expansion compatibility, mechanical compliance, and diffusion resistance through a defect‐engineered microstructure. Controlled microporosity and a defect‐assisted fcc‐to‐hcp transformation cooperatively accommodate thermal stress, while dense stacking faults and coherent lamellae generate transformation strain that mitigates interfacial damage. First‐principles calculations reveal a low stacking‐fault‐energy window near FeMn ₁₇ , together with increased Fe migration and vacancy‐formation energies, explaining the suppressed lattice diffusion. Structural analyses confirm phase stability and a clean, diffusion‐free interface after prolonged annealing. The specific contact resistivity remains below 5 µΩ cm ² , enabling a seventeen‐pair module to deliver an excellent power density of 0.26 W cm ^{− 2} and 7% efficiency at T _h = 543 K and T _c = 293 K. Thermal‐cycling and aging tests verify exceptional durability, with performance drift below 2% after 500 h and within 1% after 100 additional cycles. This work establishes a defect‐mediated strategy for constructing efficient and durable Bi ₂ Te ₃ modules, offering a transferable design paradigm for metallic barriers in thermoelectrics.