MgCuSb as a suitable electrode for contacting pre-compacted pellets of MgAgSb thermoelectric material

The p-type thermoelectric (TE) material α-MgAgSb is a promising tellurium-free bismuth telluride substitute for cooling and waste heat harvesting applications between room temperature and 573 K. Optimization of the material resulted in high values of figure of merit (<i>zT</i> _max = 1.3) to date, but performance optimization of TE devices also requires minimizing the electrical contact resistance between the TE material and the electrodes. Here, we investigate the metallization of MgAgSb with MgCuSb, providing microstructural and electrical analyses of the interfaces for functionalized legs obtained from a combined sintering of both materials systematically varying temperature, duration and pressure. Analysis of the obtained results reveals the formation of an interdiffusion layer of Ag₃Sb with varying thickness in all samples, but the contact resistance remains consistently below 10 μΩ cm². Microprobe measurements of the Seebeck coefficient indicate a change in carrier concentration in the TE material close to the interface, visualizing interdiffusion processes between MgAgSb and MgCuSb. We furthermore demonstrate that MgCuSb can successfully be applied as an electrode on pre-compacted MgAgSb samples, resulting in the first ever reported successful two-step contacting of MgAgSb. The obtained sample exhibits a strong mechanical contact without any crack at the interface, as well as a very low electrical contact resistance below 7 µΩ cm², representing less than 5% of the total leg resistance. Successful contacting of pre-compacted material is a step forward towards module fabrication as it enables better control of the TE leg length and thus device performance.