Mechanical and thermoelectric properties in Te-rich Ag2(Te,S) meta-phases

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 for wearables. 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 Ag2Te1–xSx 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 Ag2Te1–xSx. Very slight Ag-deficiency can greatly deteriorate the ductility. The thermoelectric properties of these ductile Te-rich Ag2Te1–xSx pseudobinary compounds are investigated. A maximum thermoelectric figure-of-merit of 0.6 is obtained for Ag2Te0·9S0.1 at 600 K. This work sheds light on the future investigation of Ag2(Te,S) pseudobinary compounds.