Dissociation of ⟨111⟩ dislocations on {11¯0} in pentaerythritol tetranitrate

ABSTRACT

Plastic deformation in the tetragonal explosive molecular crystal pentaerythritol tetranitrate (PETN) is mediated in part by dislocations with Burgers vector $⟨111⟩$ on $\left\{1\overline{1}0\right\}$. This observation is unexpected since $⟨111⟩$ is the longest possible Burgers vector in PETN. Moreover, plastic slip on the $\left\{10\overline{1}\right\}$ planes has not been observed. The generalised stacking fault energy surface for PETN $\left(1\overline{1}0\right)$ has been computed using dispersion-corrected density functional theory that identified a metastable stacking fault for the displacement $1/2\left[111\right]$. The stacking fault energy computed with full relaxation of the atomic positions is 83.5 mJ/m². This result indicates that dislocations with Burgers vector $⟨111⟩$ split into two partial dislocations with Burgers vector $1/2⟨111⟩$ on $\left\{1\overline{1}0\right\}$ with an equilibrium separation of about 35 and 53 Å for the screw and edge dislocations, respectively. Steric hindrance between molecules render the $1/2⟨111⟩$ stacking fault unstable on $\left\{10\overline{1}\right\}$, which prevents the dissociation of $⟨111⟩$ dislocations on these planes and accounts for why this slip system is not seen experimentally.

KEYWORDS:

• PETN
• dislocations
• plasticity
• stacking faults

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Laboratory Directed Research and Development programme of Los Alamos National Laboratory.