Interfacial reactions in Ag/Se, Ag/Se-30at%Te and Ag2Te/Se couples and the phase equilibria of the Ag-Se-Te ternary system

Abstract

Phase equilibria information of the Ag-Se-Te ternary system is important as this system is used in thermoelectric applications. The Se and Te elements are the major constituents of many thermoelectric compounds, whilst the Ag element is widely used in the thermoelectric modules as an electrode. This study examines the reaction couples of Ag/Se, Ag/Se-30at%Te and Ag2Te/Se at 350 °C, as well as the isothermal section of the Ag-Se-Te system at 350 °C. There are five three-phase regions and no ternary compounds. The Ag/Se reaction couple shows the formation of the Ag2Se reaction layer with this phase having a very homogeneous composition. The reaction is very fast. The reaction layer is 550 µm thick in the couple reacting for 2 min. The Ag2Te/Se reaction couple shows the formation of Ag2Se, liquid, and Te-rich phases. The reaction path in the Ag2Te/Se reaction couple is Ag2Te/(Se,Te)/Liquid/Ag2Se/Se. It is found that the reaction layer is 576 µm thick in the couple reacting for 2.5 min. The Ag/Se-30at%Te reaction couple shows the formation of Ag2(Se,Te) and liquid phases. A very thick reaction zone of 2600 µm is found after reacting for 2.5 min. The related reaction paths and mass balances of the reaction couples are well explained using the determined isothermal section of the Ag-Se-Te system at 350 °C.