Co/SnSe2 and (Co,Ni)/SnSe2 interfacial reactions

Abstract

BackgroundSnSe2 is a promising thermoelectric compound. Co, Ni and (Co,Ni) are barrier layer materials. Interfacial reactions are examined since they are very important for the reliability of the thermoelectric modules. MethodsCo/SnSe2 and (Co, Ni)/SnSe2 reaction couples are prepared and examined. Their reaction paths are illustrated with the Co-Se-Sn phase equilibria isothermal section and Co-Ni-Se-Sn phase equilibria isothermal tetrahedron, respectively. Significant FindingsAt both 500 °C and 300 °C, CoSe and SnSe phases are formed in the Co/SnSe2 couples. The reaction path is Co/CoSe/SnSe/SnSe2. In the (Co,Ni)/SnSe2 couples reacted at 500 °C, there are three reaction phase regions. The microstructures of these phase regions are very fine. Based on their average compositions, these three phase regions are regarded as Ni3Se2, Ni3SnSe2 and NiSnSe2 phases. But the Ni3SnSe2 and NiSnSe2 phase regions are not single-phase regions and are composed of (Co,Ni)Se+Ni3Sn2 and NiSe+SnSe phases, respectively. It is concluded among the four elements, Ni is the fastest diffusion species, Sn is the slowest, whilst Co and Se have similar diffusion rates. The results indicate Ni is not a suitable barrier layer for SnSe2 because the interfacial reactions are more significant with more Ni.