Interfacial Reactions in Ni/Sb2Te3 and Co0.2Ni0.8/Sb2Te3 Couples

Sb2Te3 is an important thermoelectric material. The interfacial reactions in the Ni/Sb2Te3 and Co0.2Ni0.8/Sb2Te3 couples are examined to verify if Ni and Co0.2Ni0.8 are suitable barrier layer materials. The Ni-Sb-Te phase equilibria isothermal sections and Co-Ni-Sb-Te isothermal tetrahedrons are proposed to provide fundamental information and for better understanding of the interfacial reactions. Only one reaction phase, lambda(2)-NiSb1-xTe2x, is observed in the Ni/Sb2Te3 couples reacted at 200 degrees C, 300 degrees C, and 400 degrees C. When reacting at 500 degrees C for 6 h, the reaction phase is lambda(1)-Ni(Sb1-xTex)(1+y). With a longer reaction time, the second phase, Ni5.66SbTe2, is formed. Note, the compositional ratios of Sb/Te of all the reaction phases remain as 2/3. The result indicates that Ni is the dominating diffusion species. The reaction results in the Co0.2Ni0.8/Sb2Te3 couples are similar to those in the Ni/Sb2Te3 couples. The reaction phase at 400 degrees C is lambda(2)-NiSb1-xTe2x , and are lambda(1)-Ni(Sb1-xTex)(1+y) + Ni5.66SbTe2 phases at 500 degrees C with a longer reaction time. The compositional ratios of Sb/Te in the reaction phases are also 2/3, and the Co contents in the reaction phases are very limited. Ni is also the dominating diffusion species in the Co0.2Ni0.8/Sb2Te3 couples.