Ni and Ag electrodes for magnesium silicide based thermoelectric generators

The development of stable and low resistance contacts between thermoelectric materials and metal bridges is indispensable for highly efficient thermoelectric generators. We have studied suitable electrode materials for n- and p-type Mg2Si1−xSnx (with x ≈ 0.6) as magnesium silicide based solid solutions are among the most promising candidates for large scale waste heat recovery applications. Evaluating in particular Ag and Ni as potential metallization, we find that Ag is a suitable electrode for p-type Mg2Si0.4Sn0.6 with a specific contact resistance of ≈10 μΩcm2 for optimized joining conditions. We also show that separating the material sintering from the joining step can be very advantageous as control over joining temperature allows tailoring of the interface composition and properties. For Ni, a reduction of the joining temperature mitigates cracking of the thermoelectric material due to the mismatch in coefficient of thermal expansion. Locally, relatively low values of 25−50 μΩcm2 for the specific contact resistances between Ni electrode and Mg2Si1−xSnx could be determined for both n- and p-type material.