Abstract
The interfacial reactions between the Ni barrier layer and the popularly used P-type (Bi0.25Sb0.75)2Te3 and N-type Bi2(Te0.9Se0.1)3 thermoelectric substrates are examined at 300 °C and 250 °C. A NiTe2 phase with significant Sb solubility, or a ternary compound, and a Bi-enriched (Bi, Sb)2Te3 phase are formed in the Ni/(Bi0.25Sb0.75)2Te3 couples. Two phases, NiTe2 and BiTe, are formed in the Ni/Bi2(Te0.9Se0.1)3 couples. Both of these two phases have significant ternary solubilities. The BiNiSbTe and BiNiSeTe phase diagrams at 300 °C are proposed based on very limited available phase diagrams of constituent binary and ternary systems. Their respective reaction paths in both couples are drawn on isothermal tetrahedrons. The average reaction rates in 10 days are 7 μm/day at 300 °C and 0.9 μm/day at 250 °C in the Ni/Bi2(Te0.9Se0.1)3 couples, and they are much faster compared to those in the Ni/(Bi0.25Sb0.75)2Te3 couples, which are 0.9 μm/day at 300 °C and 0.4 μm/h at 250 °C. It is concluded Te is the fastest diffusion species in both types of couples.
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