Mechanisms of Plastic Deformation of Metal–Organic
Framework‑5
- Publication date
- Publisher
Abstract
We
use large-scale molecular dynamics simulations to investigate
the mechanisms responsible for plastic deformation in metal–organic
framework-5 (MOF-5). Simulations of uniaxial compression along [001],
[101], and [111] directions reveal that structural collapse of {001}
planes is responsible for irreversible deformation. The process involves
slip along either one of the two ⟨100⟩ directions on
the collapsing plane; this local shear process is due to the flexibility
of the connection between of Zn–O clusters and 1,4-benzenedicarboxylate
ligands. Thus, the collapse is driven both by compressive and shear
stresses, and this fact explains the anisotropy in the mechanical
response of this cubic crystal. The development of shear-collapse
bands follows a nucleation and growth process with nuclei elongated
along the slip direction and their subsequent growth in the directions
normal to the slip and at much slower rates. This process is reminiscent
of the glide of screw dislocations. Compression along the [101] and
[111] directions led to intersection of active shear-collapse bands
and the activation of multiple ⟨001⟩{100} systems. We
also find that partially collapsed planes reduce the stiffness of
the structures, an observation that can explain discrepancies between
experimental and theoretical stiffness predictions