Figure 3. Formation energy of interstitials and vacancies in the bulk and at the boundaries, created with tilt angles of (a) 8.8°, (b) 36.8°, and (c) 53.13°, respectively.

The energy scale bar is provided. The hollow circles refer to vacancies and the solid circles to interstitials. These interstitials sites are not octahedral and tetrahedral interstitials since both are not energetically favorable. For interstitials in the bulk, energy minimization favors dumbbell defect formation around one lattice location. Close to the boundary, isolated interstitials become energetically favorable to form and corresponding stable locations are identified by allowing structural relaxations in simulations.