Distribution of N Atoms in the fcc Fe–N Interstitial Solid Solution

Monte Carlo simulations, analytical calculations and thermodynamic activity data have been combined in a study of the distribution of interstitial nitrogen atoms in the octahedral sites of the Fe–N solid solution. Two models are compared in the analysis of the Mössbauer spectra. Thermodynamic activity data are analyzed in terms of the quasichemical approximation to the statistical mechanics of interstitial solutions. The formation energies of the N–N pairs thus assessed are used as input in both Monte Carlo simulations and the quasichemical calculations. A significant discrepancy between Monte Carlo predictions and the Mössbauer results is detected. This striking effect becomes particularly important when the ordered structure model is applied in the analysis of Mössbauer data.