Abstract
(Bi1-xSbx)2Te3 and Bi2(Te1-ySey)3 are common thermoelectric materials. In the manufacturing of thermoelectric device, Sn is the major element for most of the electronic solders, and Ni is used as diffusion barrier. The interfacial reactions between Sn, Ni and (Bi1-xSbx)2Te3, Bi2(Te1-ySey)3 thermoelectric materials will be investigated in this study. The interfacial reactions at 250 oC in the Sn/(Bi0.25Sb0.75)2Te3 and Sn/Sb2Te3 couples are examined. The initial reaction product only has one phase, and is SnTe phase with small pores which are filled with liquid. With longer reaction time, the small liquid droplets connect together and form periodic liquid layer in the reaction zone. The liquid layer, which is primarily molten Sn, further reacts with Sb, and a self-assembled Sn3Sb2/SnTe alternating layer is found in the couples. Bi precipitates are found as well in the reaction zone in the Sn/(Bi0.25Sb0.75)2Te3 couples in the later stage of reactions. In Sn/Bi2(Te0.9Se0.1)3 couple, it formed SnTe, Bi6Te7, and BiTe phase. Sn/Bi2Se3 couple formed SnSe and BiSe phase. In Sn/Bi2Te3, the interfacial reaction rate is fast, and the growth rate is about 59 μm/min. It formed a irregular SnTe + Liquid phase. The amount of Se in Bi2(Te0.9Se0.1)3 substrate is only 6%, but it’s growth rate and intermetallic compound are very different compared with Sn/Bi2Te3 couple. The Ni/(Bi0.25Sb0.75)2Te3 and Ni/Bi2(Te0.9Se0.1)3 couples both formed NiTe phase, and Ni/Bi2(Te0.9Se0.1)3 also formed BiTe phase. Ni penetrates deeper in Bi2(Te0.9Se0.1)3 substrate. The fast diffusion rate may cause failure or lower the efficiency in thermoelectric device.