Morphology-Controlled Tensile Mechanical Characteristics in Graphene Allotropes

A number of graphene allotropes constructed by sp³, sp², and sp hybrid orbitals have recently been proposed to provide the broad potential for practical applications. Here, using molecular dynamics simulation, the structural and tensile characteristics of nine distinct graphene allotropes have been investigated to understand their morphology-controlled mechanical properties. Results show that the averaged out-of-plane displacement is independent of nonhexagons while being dominated by the arrangement of carbon polygons on the sheets. Each sheet possesses unique surface morphology and in-plane tensile properties that significantly vary with morphology and anisotropic crystalline orientation. Brittle, semibrittle, or ductile failure is observed, depending on the evolution of their packed polygons in facilitating tension deformation and in dissipating energy. Particularly, pentagraphene exhibits superductility as a consequence of large-scale structural transformations, accommodating stress relaxation beyond initial failure. Two distinct plastic deformation patterns in overstretched pentagraphene are uncovered, depending on the tension directions: one is dominated by structural transition from sp³-carbon-contained penta-(C₅) to mixed sp²-carbon polygons and the other is mainly controlled by a stepwise pentagon-to-hexagon transition. These findings provide physical insights into the structural evolvement of two-dimensional graphene allotropes and their effects on the mechanical properties.