First-principles studies identify a vacancy mechanism underlying the unusually high O solubility and nucleation of stable O-enriched nanoclusters in defect-containing Fe.  Oxygen, confined as an interstitial, shows an exceptionally high affinity for vacancies, an effect enhanced by spin polarization. If vacancies preexist, the O-vacancy pair formation energy essentially vanishes, allowing the O concentration to approach that of the vacancies. This O-vacancy mechanism enables the nucleation of O-enriched nanoclusters, that attract solutes with high O affinities (Ti and Y) and strengthen Fe-based alloys.

• Received 26 June 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.225502