Density functional study of structural defects in h-BNC2 sheets

Structure, energetics, electronic and magnetic properties of single and double vacancies and Stone-Wales defects in h-BNC2 sheets have been calculated using the planewave pseudopotential method within density functional theory. The formation energy of a defect strongly depends on its location within the sheet. In some cases, though not all, the energy ordering of various defects can be rationalized in terms of the strengths of various bonds that are broken or created during the defect formation. Single vacancy defects have rather low migration barriers, and the energy cost of double vacancies is smaller than that of two isolated single vacancies. Barriers of formation for Stone Wales defects at the interfaces are large, but those for healing these defects are quite small. Therefore, they can heal easily even at moderate temperatures. Thus, double vacancies are the most likely defect structures in these sheets. Many of the defects possess finite magnetic moments. Unlike BN sheets and graphene, some of the double vacancies and Stone Wales defects are also found to possess finite moment.