First-Principles Study of Microscopic Mechanism of High Ductility of Silver Sulfide/Selenide

Silver sulfide (Ag₂S) is one of the important inorganic semiconductors for industrial use because it has metal-like ductility at room temperature. On the other hand, silver selenide (Ag₂Se) does not show ductility, but has high electrical conductivity suitable for thermoelectric materials. By mixing these two chalcogenides, the development of flexible and high-performance semiconductors is expected. Experimental studies have reported that the ductility of Ag₂S_1-xSe_x mixtures is confirmed up to x = 0.6 with monoclinic Ag₂S-type structure. In order to investigate the effects of Se addition on ductility of Ag₂S, we performed simple shear deformation simulations of Ag₂S_1-xSe_x (x = 0, 0.2, 0.4, and 0.6) based on first-principles molecular dynamics method. Our simulations demonstrated that Ag₂S_1-xSe_x (x ≦ 0.6) systems have similar ductility properties to Ag₂S. Additionally, we found that the high ductility is due to the structural recovery processes occurring in the following four mechanisms: 1) spontaneous sliding of the anion-sublattice, 2) interlayer/intralayer site exchange in the anion-sublattice, 3) self-healing of fracture parts of the anion-sublattice, and 4) splitting of lines of anions into two.