Thermally Stable, Low‐Resistance Cu Alloy Contacts for Mg 3 (Sb, Bi) 2 Thermoelectric Materials by Two‐Step Contacting

Selection of suitable electrical contact is crucial for achieving low specific contact resistivity ( ρ c ) at the electrode/thermoelectric (TE) material interface. Sustaining low ρ c is far more critical than merely attaining a low value. Moreover, the conversion efficiency ( η ) and durability are often limited by unstable contact interfaces at various junctions of the TE device and the thermal stability issues of commonly used metal contacts. To address these issues, two novel Cu‐based alloys, Brass (Cu–Zn) and Manganin (Cu–Ni–Mn), were developed in this work for high‐performance n‐type Mg 3 (Sb, Bi) 2 materials. These alloys were found to exhibit very low ρ c < 5μΩ.cm 2 , with limited diffusion to Mg 3 (Sb, Bi) 2 materials after optimizing the process parameters. Even though the ρ c achieved after the conventional one‐step sintering was low, diffusion, inhomogeneity and thermal stability were shown to be bottlenecks. To solve this, a distinct two‐step contacting method was employed, and a process optimization was carried out to overcome the persisting issues and to stabilize the ρ c and η . As a result of these strategies, a high maximum conversion efficiency of η max ≈ 8.2% was achieved for Brass/Mg 3 (Sb, Bi) 2 /Brass contacts at Δ T ≈ 380 K, and showing no degradation after 15 days of thermal aging.