Process Optimization of Contact Interface Layer for Maximizing the Performance of Mg3(Sb, Bi)2 based Thermoelectric Compound

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 TE material and 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 compound 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 (ρc) by ∼ 60% is realized, without compromising TE properties. Furthermore, it was found that replacing SS powder (SSp) with SS foil (SSf) could lead to more uniform and dense layers, achieving lower specific ρcof 8.2 μΩ cm2 at the interface. A maximum conversion efficiency (ηₘₐₓ) of ~ 9.3% was obtained at temperature difference (ΔT) of ~ 380 K for SSf/Mg3(Sb, Bi)2/SSf sintered at 1073 K. Moreover, thermal aging for 30 days at 673 K confirms the robustness of SSf/Mg3(Sb, Bi)2/SSf contacts with negligible degradation of TE properties and conversion efficiency of TE single leg.