Ag-Se-Sn phase diagrams and Sn/Ag2Se interfacial reactions

Abstract

Ag2Se is a prominent thermoelectric material and Sn is a primary constituent element of joining alloys. The interfacial reactions in the Sn/Ag2Se couples at 550 °C, 400 °C and 250 °C are examined for various reaction times between 5 and 120 min. To provide fundamental understanding, the phase equilibria isothermal sections of the ternary Ag-Se-Sn system are also determined. The respective isothermal sections are proposed based on limited ternary experimental results, Ag-Se-Sn phase equilibria studies and the phase diagrams of its constituent binary systems. The reaction layers are parallel to Ag2Se substrate and grow thicker with longer reaction times and higher temperatures. Besides a thin SeSn phase layer, a thick ternary Ag8Se6Sn phase is observed in the reacted Sn/Ag2Se couples at all temperatures. Ag concentration decreases in the reaction path from Ag2Se side towards molten Sn. Hence, excess Ag is dissolved in the liquid phase and ε-Ag3Sn phase precipitates when the couple is removed from the furnace. The determined reaction path is liquid/SeSn/Ag8Se6Sn/Ag2Se for all temperatures.