Ni-Pb-Te phase equilibria and interfacial reactions in Ni/PbTe couples

Background

PbTe is an important thermoelectric compound. Ni is commonly used as a barrier layer. To provide fundamental information, an Ni-Pb-Te phase equilibria isothermal section at 650 °C and Ni/PbTe interfacial reactions at 650 ^oC, 500 ^oC and 400 ^oC are determined.

Methods

The isothermal section is proposed based on results of equilibrated alloys and related phase diagrams. The interfacial reactions are examined using reaction couples.

Significant Findings

There is no ternary compound. At 650 ^oC, the liquid phase extending from the Pb corner has significant symmetrical solubilities of Ni and Te, and displays a peculiar deep and narrow shape. No interfacial reactions are observed in the Ni/PbTe couple heat-treated at 500 ^oC and 400 ^oC for a month. However, significant reactions are observed when reacted at 650 ^oC. Reaction zone thickness is 120 μm when reacted for 30 min. The reaction zone has many phases, and yet has clear phase region boundaries. Liquid and β-Ni₃Te₂ phases are formed, and the reaction path is Ni/β-Ni₃Te₂+Liquid (I)/Liquid (I)/PbTe. Many phases were formed from solidification when the couple was removed from a furnace. Ni is the dominating diffusion species in the Ni/PbTe couples. Ni penetrates into the PbTe substrate, reacts with Te to form Ni₃Te₂, and the liquid phase is formed with excess Pb.