Interfacial Reactions in Ni/Se-Sn, Ni/Se-Te, Ni/Sn-Te and Ni/Se-Sn-Te Couples

SnSe-, SnTe- and Se-Sn-Te-based alloys are important materials for thermoelectric and optical recording applications and Ni is highly recommended as barrier layer material. In this study, the interfacial reactions in Ni/SnSe, Ni/Se_xTe_1−x, Ni/SnTe, and Ni/SnTe_0.9Se_0.1 are systematically investigated to provide fundamental understanding. The substrates are prepared with pure constituent elements and electroplated with a layer of Ni. The reaction couples are heat-treated, and their reaction phases are determined. Based on assessment of the literature results, the phase equilibria isothermal sections of the related material systems are proposed. The reaction paths in these couples are determined and illustrated with the proposed isothermal sections. The reaction paths in the Ni/SnSe couple reacted at 250°C and 300°C are both Ni/Ni₃Sn/Ni₃Sn₂/NiSe/Ni_5.62SnSe₂/Ni₃SnSe/ NiSnSe/SnSe. Both NiSnSe and Ni₃SnSe are likely metastable ternary phases formed by rapid diffusion of Ni atoms into the SnSe substrate. The reaction path in the Ni/Se_xTe_1−x couples reacted at 200°C is Ni/Ni₃Te₂/τ/Se_xTe_1−x and in the Ni/SnTe couples reacted at 400°C is Ni/Ni₃Sn/Ni₃Sn₂/Ni_5.78SnTe₂/Ni₃SnTe₂/SnTe. In the Ni/SnTe_0.9Se_0.1 couple reacted at 400°C, the reaction path is the same as that of Ni/SnTe. The reaction rates decrease with lower reaction temperatures, and the reaction zone grows thicker with longer reaction time. Based on the morphology and reaction phase sequences, it is concluded Ni is the fastest diffusion species in the diffusion couples among Ni, Se, Sn and Te.