Bending the rules: Strain accommodation in layered crystalline solids through nanoscale buckling over dislocations

Abstract

Basal dislocations and ripplocations both offer explanations for the deformation of layered crystalline solids in response to compressive strain. Existing work, however, presents no clear definition of a ripplocation and the distinction between these two mechanisms remains unclear. Molecular dynamics simulations in graphite and modified graphitic models reveal that equivalent additional half-planes of material can induce both dislocations and ripplocations. In this work, we find that ripplocations are essentially an elastic buckling phenomenon operating at the atomic scale, rather than a discrete crystallographic defect. Dislocation core confinement produces incommensurate planar elastic strains with sufficient energy to trigger a buckling instability that transfers strain energy to the surrounding lattice. The interplay between incommensurate strain and buckling is a quasi-continuum phenomenon where both mechanisms may accommodate arbitrary disregistry, not only the discrete values accommodated by perfect or partial basal dislocations. The mechanistic transition depends critically on the atomic-scale interfacial energies between layers and the continuum elastic behavior of the bulk material. Buckling is possible, though unfavorable, in the MAX phase Ti3AlC2 and systems of multiple layers buckle at lower strains than only a single layer. These extensions of the ripplocation model in van der Waals layered solids suggest that nanoscale elastic buckling potentially plays a role in the deformation of a wide range of layered crystalline systems in response to common mechanical configurations.