DFT study of nitrogen–vacancy complexions in (fcc) Fe

Abstract

Formation energies of nitrogen (N)/vacancy (v) monomers, N–N and N–v dimers and N–v complexions in an ideal face-centered cubic (fcc) lattice of iron are obtained via DFT calculations. Based on a thermodynamic model, the occupancies of various complexions and the vacancy concentration as a function of the chemical potential of N and temperature T are predicted. We found that increasing the chemical potential or content of N can increase the vacancy concentration considerably, e.g. compared with the case without nitrogen, increasing the N content to 10 at% at 750 K can increase the vacancy concentration by about eight orders of magnitude when a saturated concentration is reached.

Nitrogen diffusion in vacancy-rich ferrite and austenite, from first principles to applications

“…However, there is limited DFT literature which investigates the dilute-solute case, which is known experimentally to have a distinctly larger energy barrier for diffusion 1.74 eV = 167 kJ mol −1 [13]. Both nitrogen [14] and carbon [15] energy barriers are found to be consistently overestimated from DFT calculations using non-magnetic FCC iron, exceeding their experimental evaluations by more than 0.5 eV = 48.2 kJ mol −1 . Discrepancies of this magnitude are peculiar, since at temperatures where austenite is in thermodynamic equilibrium, the magnetic contribution to diffusion energy barriers should be relatively small.…”

“…In previous DFT literature, the energy barriers for nitrogen diffusion in the proximity of vacancies have been explored for both ferromagnetic BCC [16] and anti-ferromagnetic FCC [14] iron. Moreover, experimental approaches such as resistivity recovery [17] and irradiation [18] have been used to calculate nitrogen-vacancy trapping enthalpies in α Fe.…”

A comparative investigation of the behaviors of H in Au and Ag from first principles

“…It is widely believed that even a very small number of impurity atoms (e.g. only a few parts per million) may lead to significant variation of materials [1][2][3][4][5][6]. Accordingly, analyzing the properties of impurities in materials is quite useful for understanding the microstructure changes of materials caused by impurities.…”