Reaction evolution and alternating layer formation in Sn/(Bi0.25Sb0.75)2Te3 and Sn/Sb2Te3 couples

(Bi-1 Sb-x(x))(2)Te-3 is important for thermoelectric applications, and Sn is the major element for most electronic solders. This study examines interfacial reactions in the Sn/(Bi0.25Sb0.75)(2)Te-3 and Sn/Sb2Te3 couples at 250 degrees C. It has been observed that the interfacial reaction rates are extremely fast, and the growth rates of the layers are 27 mu m/min and 19 mu m/min, respectively. The initial reaction product is SnTe phase with nano-size pores which are filled with liquid. With prolonged reaction time, the nano-size 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 reacted for longer than 15 min. Bi precipitates with feature size less than one micron are found as well in the reaction zone in the Sn/(Bi0.25Sb0.75)(2)Te-3 couples in the later stage of reactions. The alternating layer and Bi precipitates result from supersaturation of Sb and Bi in the reaction layer caused by the fast in-flux of Sn. (C) 2012 Elsevier B. V. All rights reserved.