Interfacial reaction between Nb foil and n-type PbTe thermoelectric materials during thermoelectric contact fabrication

PbTe is a high-conversion-efficiency thermoelectric (TE) material that is commonly used in space exploration applications. Integration of PbTe in TE devices has a significant impact on the conversion efficiency and reliability of TE devices. Hence, our effort focuses on developing novel approaches for bonding metallic contacts to PbTe to improve device performance and reliability. In this study, pure Nb foil was directly bonded to PbTe-based TE materials to fabricate the hot-side contacts of TE elements using a rapid hot-press. The materials were sintered at 700°C under pressure of 40 MPa for various holding times. We found that a reaction layer of needle-like Nb₃Te₄ mixed with Pb forms at the interface of the Nb/PbTe joints and that Pb is distributed in the gaps of the Nb₃Te₄ grains. We analyze the resulting microstructure and finally calculate the time exponent of the growth kinetics of the Nb₃Te₄ layer. Fracture surface analysis showed that the Nb/PbTe joint fractures at the interface between Nb and Nb₃Te₄ and within the PbTe matrix, indicating that the bonding between Nb and Nb₃Te₄ is weak.