Temperature-dependent mechanical properties and the microscopic deformation mechanism of bilayer γ -graphdiyne under tension.

γ -graphdiyne ( γ -GDY) is a new two-dimensional carbon allotrope that has received increasing attention in scientific and engineering fields. The mechanical properties of γ -GDY should be thoroughly understood for realizing their practical applications. Although γ -GDY is synthesized and employed mainly in their bilayer or multilayer forms, previous theoretical studies mainly focused on the single-layer form. To evaluate the characteristics of the multilayer form, the mechanical properties of the bilayer γ -GDY ( γ -BGDY) were tested under uniaxial tension using the molecular dynamics simulations. The stress-strain relation of γ -BGDY is highly temperature-dependent and exhibits a brittle-to-ductile transition with increasing temperature. When the temperature is below the critical brittle-to-ductile transition temperature, γ -BGDY cracks in a brittle manner and the fracture strain decreases with increasing temperature. Otherwise, it exhibits ductile characteristics and the fracture strain increases with temperature. Such a temperature-dependent brittle-to-ductile transition is attributed to the interlayer cooperative deformation mechanism, in which the co-rearrangement of neighboring layers is dominated by thermal vibrations of carbon atoms in diacetylenic chains. Furthermore, the brittle-to-ductile transition behavior of γ -BGDY is independent of loading direction and loading rate. The ultimate stress and Young's modulus decrease at higher temperatures. These results are beneficial for the design of advanced γ -GDY-based devices.