By combining density functional theory, empirical potential, and atomic transport model approaches, an investigation was made of the energetics and the diffusion properties of P interstitials in dilute Fe-P alloys. Although P was a substitutional impurity in α-Fe, when a self-interstitial atom approaches a substitutional P, the P atom became interstitial with an energy gain of up to 1.0eV . The octahedral and the ⟨110⟩ mixed dumb-bell were the lowest-energy configurations with similar stabilities. The P atoms were highly mobile in both configurations. The transitions between these two configurations also required low activation energies. The most likely mechanisms leading to long-distance diffusion of a P interstitial were proposed by ab initio calculations. The resulting effective diffusion energy estimated by the transport model was 0.19eV , which agreed with the result from resistivity recovery experiments, suggesting that the Fe-P mixed dumb-bells were more mobile than the self-interstitial atoms. The fast-migrating P interstitial could be deeply trapped by a substitutional P atom. The resulting complexes were very stable with a binding energy of around 1.0eV . Their mobilities were investigated by means of the dimer method using an Fe-P empirical potential. A comparison between the present predictions and existing experimental results was also made.

Theoretical Study of Atomic Transport via Interstitials in Dilute Fe-P Alloys. E.Meslin, C.C.Fu, A.Barbu, F.Gao, F.Willaime: Physical Review B, 2007, 75[9], 094303