Nitrogen vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in B1 TiN studied by ab initio and classical molecular dynamics with optimized potentials

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2015-02, Vol.91 (5), p.054301
• Main Authors: Sangiovanni, D G, Alling, B, Steneteg, P, Hultman, L, Abrikosov, I A
• Format: Article
• Language: English
• Subjects: Chemical bonds; Diffusion; Lattice vacancies; Lattices; Molecular dynamics; Point defects; Self-interstitials; Simulation; Tin
• ISSN: 1098-0121; 1550-235X; 1550-235X
• DOI: 10.1103/PhysRevB.91.054301

We use ab initio and classical molecular dynamics (AIMD and CMD) based on the modified embedded-atom method (MEAM) potential to simulate diffusion of N vacancy and N self-interstitial point defects in B1 TiN. TiN MEAM parameters are optimized to obtain CMD nitrogen point-defect jump rates in agreement with AIMD predictions, as well as an excellent description of TiN sub(x) (~0.7 < x [< or =] 1)elastic, thermal, and structural properties. We determine N dilute-point-defect diffusion pathways, activation energies, attempt frequencies, and diffusion coefficients as a function of temperature. In addition, the MD simulations presented in this paper reveal an unanticipated atomistic process, which controls the spontaneous formation of N self-interstitial/N vacancy (N super(I)/N super(V))pairs (Frenkel pairs), in defect-free TiN. This entails that the N lattice atom leaves its bulk position and bonds to a neighboring N lattice atom. In most cases, Frenkel-pair N super(I) and N super(V) recombine within a fraction of ns; ~50% of these processes result in the exchange of two nitrogen lattice atoms (N - N super(Exc)). Occasionally, however, Frenkel-pair N-interstitial atoms permanently escape from the anion vacancy site, thus producing unpaired N super(I) and N super(V) point defects.