An electronic view on dislocation nucleation in diamond

Plastic deformation in crystals is governed by the nucleation and motion of dislocations, for which generalized stacking fault energy (GSFE) provides an effective energetic nucleation criterion in metals. However, in superhard covalent crystals such as diamond, the high critical elastic strain causes the lattice configuration at plastic initiation to deviate significantly from equilibrium, rendering the lattice model used in GSFE calculations uncertain and thereby limiting the applicability of traditional GSFE criteria. Here, by analyzing the evolution of atomic configurations and their associated electronic distributions during dislocation glide, we show that local metallization at the dislocation core, manifested by the emergence of transferrable conduction electrons, is a prerequisite for dislocation glide in diamond. We identify a critical bandgap of approximately 1.12 eV in the diamond lattice, below which a dislocation core region with intrinsic elastic strain field may undergo local metallization. This bandgap threshold, reached prior to lattice instability, serves as a generalizable indicator of the brittle-to-ductile transition in covalent materials under arbitrary stress states, overcoming the limitations of traditional GSFE-based criteria.