First-principles investigation of oxygen interstitial solubility, site preference, and nucleation behavior in BCC-Fe doped with rare earth elements (Y, La, Ce)

The effects of rare earth element doping (Y, La, and Ce) on the solubility, clustering, and migration behavior of interstitial oxygen atoms in body-centered cubic (BCC) iron were systematically investigated using density functional theory (DFT) calculations. The results reveal that Y and Ce exhibit higher thermodynamic stability and solubility in BCC-Fe, while rare earth doping significantly reduces the solution energy of oxygen atoms at the second-nearest neighbor (2NN) octahedral sites of rare earth atoms and promotes their effective binding. And oxygen atoms in rare earth-doped Fe crystals preferentially occupy the 2NN octahedral interstitial sites relative to the rare earth atoms, with the Y-doped system displaying the strongest oxygen solubility and electron-donating characteristics. Furthermore, an energy convex hull analysis was proposed to predict the initial coordination configurations of rare earth oxides, with predictions in good agreement with experimental data. Analyses of binding energies and energy convex hulls indicate that different rare earth dopants substantially affect the pairing sequence of oxygen clusters and the initial coordination structures during nucleation, with the predicted Y-O, La-O, and Ce-O bond lengths and coordination numbers closely matching experimental results. Migration energy barrier calculations demonstrate that rare earth elements can effectively reduce the migration barriers of oxygen atoms, promoting their segregation to more stable configurations. This study elucidates the atomic-scale mechanisms by which rare earth elements regulate solute-oxygen multiplet interactions in iron-based materials, providing a theoretical foundation for the design of high-performance ODS steels and rare earth-strengthened iron-based alloys.