Ductile Ag₂(Te,S) pseudobinary compounds have attracted great attention in thermoelectric community since they can be fabricated into high-performance flexible and hetero-shaped thermoelectric devices. However, in spite of the numerous studies, the ‘brittle–ductile’ transition boundary in Ag₂(Te,S) is still unclear. In this work, a series of Te-rich Ag₂(Te,S) pseudobinary compounds have been prepared. The structure characterizations confirm they belong to the new-concept of meta-phase. The systematically investigation on the mechanical properties demonstrate that the ‘brittle–ductile’ transition boundary appears around x = 0.1. Unexpected good ductility is observed in the Te-rich Ag₂Te_1-xS_x crystalizing in the Ag₂Te room-temperature monoclinic structure and high-temperature cubic structure, which are thought to be brittle before. Likewise, Ag content is found to be a very critical parameter determining the ductility of Te-rich Ag₂Te_1-xS_x. Very slight Ag-deficiency can greatly deteriorate the ductility. The thermoelectric properties of these ductile Te-rich Ag₂Te_1-xS_x pseudobinary compounds are investigated. A maximum thermoelectric figure-of-merit of 0.6 is obtained for Ag₂Te_0.9S_0.1 at 600 K. This work sheds light on the future investigation of Ag₂(Te,S) pseudobinary compounds.

AgSbTe₂-based ternary chalcogenides show excellent thermoelectric performance at low- and middle-temperature ranges, yet their practical applications are greatly limited by their intrinsic poor thermodynamic stability. In this work, we demonstrate that AgSbTe₂-based ternary chalcogenides can be stabilized for service below their decomposition threshold. A series of Ag_xSb_2-xTe_3-x (x = 1.0, 0.9, 0.8 and 0.7) samples have been prepared by the melt-quenching method. Among them, phase pure Ag_0.9Sb_1.1Te_2.1 is verified by comprehensive structural characterizations from macroscale by X-ray diffraction to microscale by energy-dispersive spectroscopy and then to sub-nanometer scale by atom probe tomography. This composition is further chosen for the stability investigation. The decomposition threshold of Ag_0.9Sb_1.1Te_2.1 appears around 473 K. Below this temperature, the chemical compositions and thermoelectric properties are barely changed even after 720 h annealing at 473 K. The figure-of-merit (zT) value of Ag_0.9Sb_1.1Te_2.1 below the decomposition threshold is very competitive for real applications even compared with Bi₂Te₃-based alloys. The average zT of Ag_0.9Sb_1.1Te_2.1 at 300–473 K reaches 0.84, which is higher than most other thermoelectric materials in a similar temperature range, promising applications in miniaturized refrigeration and power generation near room temperature.