Origin of ductility in amorphous Ag2S0.4Te0.6

Amorphous Ag2S0.4Te0.6 shows outstanding ductility and promising thermoelectric properties at room temperature [He et al., Sci. Adv. 6, eaaz8423 (2020)], while the origin of its exceptional ductility is still not very clear. Here, we systematically investigate the temperature-dependent structure and thermodynamic behavior of the Ag2SxTe1-x (x = 0-1.0) system by means of in situ x-ray powder diffraction and dynamic thermodynamic analysis, respectively. Our experimental results reveal that the degree of crystallization in Ag2SxTe1-x varies continuously with the ratio of S and Te. The Ag2S0.4Te0.6 sample is composed of two amorphous phases, i.e., the S-rich and Te-rich Ag-2(S,Te) glasses. The S-rich Ag-2(S,Te) amorphous phase with the atomic ratio about Ag:S:Te = 66:21:13 is identified as the ductile phase, which is the origin of ductility in the Ag2S0.4Te0.6 sample. The Ag2S-based glass in the supercooled liquid state at room temperature behaves like a Newtonian fluid at low strain rates, leading to the excellent ductility of Ag2S0.4Te0.6. Our work demonstrates the great potential to design and realize flexible inorganic functional materials through amorphization.