Fabrication and reliability evaluation of Yb0.3Co4Sb12/Mo–Ti/Mo–Cu/Ni thermoelectric joints

Joining p- and n-type thermoelectric materials with electrodes is the key technique to fabricate a thermoelectric device. Due to its large oxidation resistance and good weld adaptability, Ni is a good electrode material in practical applications. However, the diffusion between Ni and skutterudite thermoelectric materials limits its application in fabricating a skutterudite-based device. In this study, Mo–Cu and Mo–Ti alloys were designed as the buffer and barrier layers respectively to join Ni electrodes with Yb0.3Co4Sb12 by a one-step spark plasma sintering process. A thermal shock test between 25 °C and 550 °C allowed us to conclude that Mo55Cu45 alloy is the most suitable buffer layer, which can greatly reduce thermal residual stress. The influence of Mo content on the evolution of the Mo–Ti/Yb0.3Co4Sb12 interfacial microstructure and electrical contact resistance during the accelerated aging at 550 °C was studied. After adding a small amount of Mo to Ti, the growth rate of the diffusion layer between Ti and Yb0.3Co4Sb12 decreased. The contact resistivity remained below 9 μΩ cm2 after 12 days of aging at 550 °C, indicating that the joints had high thermal duration stability. However, excess Mo will lead to a CTE mismatch between Mo–Ti and Yb0.3Co4Sb12. Thus, it has been concluded that 5 at% of Mo is the optimum composition.