Phase equilibria of Ag-Sb-Te thermoelectric materials

The ternary Ag-Sb-Te system is important for thermoelectric applications because the AgSbTe2 ternary compound has a high figure-of-merit and because Ag-Sb-Te is a subsystem of the very promising quaternary Pb-Ag-Sb-Te thermoelectric alloys. In this study we prepared equilibrated Ag-Sb-Te ternary alloys at 250 and 400 °C. These alloys were metallographically examined, and their microstructures and equilibrium phases were determined. Based on the phase equilibria information available in the literature and the experimental results determined in this study, the isothermal sections of the ternary Ag-Sb-Te system at 250 and 400 °C were constructed. The AgSbTe2 compound is stable at 400 °C but not at 250 °C. Moreover, high-resolution transmission electronic microscopy images of the ternary AgSbTe2 compound and its crystal structure were determined. The crystal structure of AgSbTe2 is rock salt (NaCl type), and its homogeneous compositional regime is determined to be 49.0-53.0 at.% Te and 28.0-30.0 at.% Sb. The solubilities of Ag in the Sb-Te binary compounds, γ and δ, at 400 °C are as high as 8.6 and 5.7 at.%, respectively.