Interfacial Reactions in Ni/Sb₂Te₃ and Co_0.2Ni_0.8/Sb₂Te₃ Couples

Sb₂Te₃ is an important thermoelectric material. The interfacial reactions in the Ni/Sb₂Te₃ and Co_0.2Ni_0.8/Sb₂Te₃ couples are examined to verify if Ni and Co_0.2Ni_0.8 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, λ₂-NiSb_1−xTe_2x, is observed in the Ni/Sb₂Te₃ couples reacted at 200°C, 300°C, and 400°C. When reacting at 500°C for 6 h, the reaction phase is λ₁-Ni(Sb_1−xTe_x)_1+y. With a longer reaction time, the second phase, Ni_5.66SbTe₂, 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 Co_0.2Ni_0.8/Sb₂Te₃ couples are similar to those in the Ni/Sb₂Te₃ couples. The reaction phase at 400°C is λ₂-NiSb_1−xTe_2x , and are λ₁-Ni(Sb_1−xTe_x)_1+y + Ni_5.66SbTe₂ phases at 500°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 Co_0.2Ni_0.8/Sb₂Te₃ couples.