Interaction between oxygen and yttrium impurity atoms as well as vacancies in fcc iron lattice: Ab initio modeling

Synthesis of advanced radiation-resistant steels as construction materials for nuclear reactors, which contain the uniformly distributed yttria precipitates (ODS steels), is an important task for ecological security of nuclear plants. The initial stage of theoretical simulation on oxide cluster growth in the steel matrix is a large-scale ab initio modeling on pair- and triple-wise interaction between the Y and O impurity atoms as well as Fe vacancies, including their different combinations, in the paramagnetic face-centered-cubic (fcc) iron lattice. Calculations on the pair of Y atoms have shown that no bonding appears between them, whereas a certain attraction has been found between Y substitute atom and Fe vacancy. Inter-defect bonding is also formed between the impurity atoms in Y-O and O-O pairs. These calculations have led to the assumption that inclusion of O atom is necessary to form a stable bonding between the impurity atoms, however, the calculations of Y-O-Y defect cluster (where O atom is positioned in the interstitial position), have shown that it is not enough. The main conclusion from these calculations is that the role of Fe vacancies in the inter-defect bonding is quite significant, which was proved by the calculations of Y-O-Y cluster with O atom in the substitute position as well as by the calculations of the Y-V _Fe-Y cluster.