Liquidus Projection of the Ag-Sn-Te Ternary System

Abstract

The Ag-Sn-Te ternary system is of interest to thermoelectric applications and its liquidus projection is determined in this study. Forty Ag-Sn-Te ternary alloys are prepared and their primary solidification phases are determined. These different primary solidification phase regions include three terminal solid solutions: Ag, Sn, and Te; six binary intermediate phases: SnTe, β-Ag5Te3, Ag1.9Te, Ag2Te (assuming no phase transformation), ζ-Ag4Sn, and e-Ag3Sn; and one ternary compound, AgSnTe2. These data, together with the phase diagrams of the three constituent binary systems, are employed to construct the univariant lines of the liquidus projection. The temperature-descending directions of these univariant lines are determined using thermal analysis results and mass balance concept. The types of invariant reactions and the reaction temperatures are determined from the temperature-descending directions of the univariant lines and by thermal analysis. There are two Class I reactions, five Class II reactions, and one Class III reaction. The invariant reaction with the highest reaction temperature is L + Ag = Ag2Te + e-Ag3Sn, at 992.7 ± 4 K (719.5 ± 4 °C), and that with the lowest reaction temperature is L = Sn + e-Ag3Sn + SnTe, at 494.2 ± 4 K (221 ± 2 °C).