Investigation on the decomposition behavior of AgSbTe₂-based chalcogenides

Recently, AgSbTe₂-based ternary chalcogenides have attracted great attention in thermoelectric community due to their high figure-of-merits at the middle-temperature range, but their stability has raised huge controversy. Some literatures reported inconsistent and even contradictory results on their stability. In this work, taking Ag_0.9Sb_1.1Te_2.1 as an example, we systematically investigate its decomposition behavior to explore the stability of AgSbTe₂-based chalcogenides. Obvious decomposition is observed for Ag_0.9Sb_1.1Te_2.1 between 473–643 K, but the decomposition rate does not monotonously vary with increasing temperature. The rapidest decomposition rate occurs around 573 K. Ag_0.9Sb_1.1Te_2.1 does not directly decompose into Ag₂Te and Sb₂Te₃. A layered Ag–Sb–Te ternary phase with diverse stacking units exists as the intermediate decomposition product and the transformation from it to the final Sb₂Te₃ needs very long duration. In addition, the decomposition products can regenerate into the pure AgSbTe₂-based cubic phase above the decomposition temperature range. Finally, a qualitative Time-Temperature-Transformation diagram is plotted for Ag_0.9Sb_1.1Te_2.1, which can intuitively illustrate its thermodynamic- and kinetic-controlled decomposition behavior. This work might be able to end the long-term controversy on the stability of AgSbTe₂-based chalcogenides and guide the development of stable compounds in the future.