Process optimization of contact interface layer for maximizing the performance of Mg3(Sb,Bi)2 based thermoelectric compounds†

Abstract

Mg₃(Sb,Bi)₂ based compounds exhibit promising thermoelectric (TE) performance within the 300–700 K range, making them suitable for mid-temperature applications; yet achieving optimal electrical contact between the TE material and the contact material is crucial. One-step sintering has emerged as a widely used technique for establishing these contacts in Mg₃(Sb,Bi)₂ compounds, though variations in process parameters can impact contact quality and, consequently TE conversion efficiency. Therefore, this study explores the optimization of Mg₃(Sb,Bi)₂ compounds using spark plasma sintering with stainless steel (SS) 304 contacts at three different temperatures of 973 K, 1023 K, and 1073 K. By increasing the sintering temperature from 973 K to 1073 K, a significant reduction in the specific contact resistivity (ρ_c) by ∼60% is realized, without compromising TE properties. Furthermore, it was found that replacing SS powder (SS_p) with SS foil (SS_f) could lead to more uniform and dense layers, achieving a lower specific ρ_c value of 8.2 μΩ cm² at the interface. A maximum conversion efficiency (η_max) of ∼9.3% was obtained at a temperature difference (ΔT) of ∼380 K for SS_f/Mg₃(Sb,Bi)₂/SS_f sintered at 1073 K. Moreover, thermal aging for 30 days at 673 K confirms the robustness of SS_f/Mg₃(Sb,Bi)₂/SS_f contacts with negligible degradation of TE properties and conversion efficiency of the TE single leg.