Transmission electron microscopy study of an electron-beam-induced phase transformation of niobium nitride

Tetragonal γ-NbN1 − x was irradiated with 300 keV electrons at room temperature to fluences from 1.8 × 1024–5.4 × 1026 e/m2. The superlattice structure in γ-NbN1 − x was observed using transmission electron microscopy and found to disappear at a fluence of 5.4 × 1026 e/m2. During this process, displaced nitrogen atoms occupy vacant sites on the nitrogen sublattice. The final structure is a δ-phase (B1) structure. A randomized arrangement of N vacancies is responsible for the observed γ → δ transformation.