Manipulation of giant negative Poisson's ratios in three-dimensional graphene networks

Three-dimensional (3D) graphene networks (3DGNs) have drawn broad interest recently for their superior physical properties, such as large surface area, high strength, superelasticity, tunable band gaps and topological properties, with potential applications in high-capacity energy storage and novel electronic systems. In this work, giant negative Poisson ratios (NPRs) up to $\ensuremath{-}8.5$ and colossal auxetic transverse contraction (or expansion) of more than 40% (or 20%) in 3DGNs are predicted by first-principles calculations, adding another extraordinary mechanical property to 3DGNs. A mechanism dominated by ${sp}^{3}$-carbon bond angle distortion and in-plane anisotropy variation is revealed that can explain such exceptional NPRs in 3DGNs. Furthermore, easy manipulation and enhancement of NPRs are achieved by applying biaxial stresses which increase the in-plane anisotropy of 3DGNs, providing a way for the rational design and application of NPR materials. These discoveries will deepen our understandings of 3DGNs and broaden their technological applications as multifunctional materials.