Kinetic study of solid-state interfacial reactions of p-type (Bi,Sb)2Te3 thermoelectric materials with Sn and Sn–Ag–Cu solders

Abstract

P-type (Bi,Sb)2Te3 material system is extensively used in commercial thermoelectric (TE) applications. Soldering is commonly applied to fabricate bulk TE elements into TE modules. This study carefully examined the solid-state interfacial reactions of the commercial (Bi,Sb)2Te3 substrate with Sn and Sn–3.0Ag–0.5Cu solders. The joining plane was along the c-axis of the highly oriented [1 1 0] TE substrate. For the reactions with pure Sn solder, both the intermetallic compounds (IMCs) of SnTe and SnSb were rapidly formed at the interface. Most importantly, it was clearly demonstrated that both of them exhibited a linear growth with the aging time. The growth rates of SnTe and SnSb were 15.1 μm/h and 4.3 μm/h, respectively, at 180 °C. The IMC growth kinetics was further investigated systematically. The activation energies for the SnTe and SnSb growths were 151.6 kJ/mol and 165.3 kJ/mol, respectively. For the Sn–3.0Ag–0.5Cu/(Bi,Sb)2Te3 reaction, the SnTe and SnSb were also formed simultaneously. Similarly, they also had a linear growth, but their growth rates were significantly suppressed. A thin stripe-like Ag-rich phase was formed at the SnTe/(Bi,Sb)2Te3 interface, which could be the cause of the suppression of IMC growth. Additionally, minor addition of 0.1 wt.% Ga in Sn was also found to effectively suppress the interfacial IMC growth.