Abstract
The crystal-structure deformation depending on lattice parameters in ANB8-N compounds is investigated on the basis of density-functional theory (DFT) calculations. Our DFT calculations for C, BN and BeO demonstrate that the energy difference in cohesive energy along crystal structure deformation path strongly depends on the ionicity 𝑓i of materials. In particular, the energy barriers for structural deformation from threefold coordinated (hexagonal graphite) to fourfold coordinated (wurtzite) structures in BN and C are marked, whereas that in BeO is negligible. The difference in the energy barrier originates from both repulsive interaction among bond charges and attractive interaction among ionic charges. The repulsive interaction among bond charges in C (𝑓i = 0) results in the highest energy barrier of 0.39 eV, while the attractive interaction among ionic charges in BeO with large ionicity (𝑓i = 0.602) does in quite small energy barrier. These results imply that the ionicity is crucial for determining the energy change along crystal deformation path as well as the structural stability. [DOI: 10.1380/ejssnt.2014.79]
