Enhanced Interfacial Reliability and Mechanical Strength of CoSb₃-Based Thermoelectric Joints with Rationally Designed Diffusion Barrier Materials of Ti-Based Alloys

To achieve high-performance thermoelectric (TE) devices, constructing a good interfacial connection between TE materials and electrodes is as important as having high figure-of-merit TE materials. Although CoSb3-based TE devices have received great attention for power generation recently, the limited long-term service stability is the main obstruct for their applications. In this work, we have prepared two kinds of Ti-based alloys (Ti83.7Al10.7Si5.6 and Ti74Ni26) as the diffusion barrier layer of CoSb3-based TE joints by the spark plasma sintering method and have systematically investigated their interfacial behaviors during the aging process. The performances of contact resistivity and mechanical strength for Ti74Ni26/Yb0.4Co3.8Fe0.2Sb12 TE joints are good before aging treatment but gradually deteriorate during the aging process, which should be ascribed to the phase-transition-induced negative thermal expansion in Ti–Ni alloys. On the other hand, Ti83.7Al10.7Si5.6/Yb0.4Co3.8Fe0.2Sb12 TE joints show both low contact resistivity (<10 μΩ·cm2) and high mechanical strength (>20 MPa) before and after 16-day aging at 500 °C, which is originated from the matching of the coefficient of thermal expansion (CTE) and the formation of network structures in Ti–Al–Si alloys. We have also prepared an eight-couple TE module of p-Ge0.9Sb0.1TeB0.01/n-Yb0.4Co3.8Fe0.2Sb12 and have measured its corresponding device performance. Our work has demonstrated that the matched CTE and network structures in the Ti–Al–Si alloy are key to obtain high-performance CoSb3-based TE joints for long-term service.