Co-Sb-Te Phase Equilibria and Co/Sb2Te3 Interfacial Reactions

Sb₂Te₃ is an important thermoelectric material. Co is a potential diffusion barrier. This study examined the electroplated Co/Sb₂Te₃ interfacial reactions at 300  °C, 400 °C and 500 °C. To provide fundamental information and for better understanding the reaction paths, the Co-Sb-Te phase equilibria isothermal sections at these three temperatures are proposed. No ternary compound is found. The 400 °C isothermal section contains (Co), (Sb), (Te), β-CoSb, β-Co_1−xTe, CoSb₃, δ-(Sb₂Te), γ-(SbTe), Sb₂Te₃ and a continuous solid solution γ-Co(Sb,Te)₂. At 500 °C, except for Te being molten, the phase relationships are similar to those at 400 °C. At 300 °C, although γ-CoSb₂ and γ-CoTe₂ have very significant mutual solubilities, they are two separate phases and do not form a continuous solid solution. In the Co/Sb₂Te₃ couple reacted at 300 °C, only one reaction phase, γ-CoTe₂ with Sb solubility, is formed. Similar results are found in the Co/Sb₂Te₃ couple reacted 400 °C, and the reaction phase is the continuous solid solution γ-Co(Sb,Te)₂. Two reaction phases, β-Co_1-xTe and γ-Co(Sb,Te)₂, are found in the couple reacted at 500 °C. The compositional ratio of Sb/Te in the reaction phase remained at 2/3 indicates that Co is the dominating diffusion species. The reaction phases are formed rapidly by Co penetration into the Sb₂Te₃ substrate. A peculiar phenomenon was found with the reaction layer that formed on the side of Co that was not in direct contact with the Sb₂Te₃ substrate which will be further investigated.