Interaction of O-Y and O-Y-Ti clusters embedded in bcc Fe with He, vacancies and self-interstitial atoms.

Calculations based on density functional theory are performed to investigate the interaction of O-Y and O-Y-Ti clusters in bcc Fe with He atoms, vacancies (v) and self-interstitial atoms (SIA). The four different cluster structures studied in our previous work (J. Phys.: Condens. Matter 31 095701) are considered. He, v and SIA are inserted on different positions inside and in the environment of the clusters, the total energy of the corresponding supercell is minimized and the binding and incorporation energy of the three kinds of defects is determined. He in the center of a cage-like (CL) cluster is more stable than on interfacial vacant sites (IVS). In CL O-Y clusters He on an IVS is more stable than in the cluster structure with oxygen in the center, whereas there is no significant difference between the two kinds for clusters with Ti. Up to a distance of 1.5 times the iron lattice constant from the cluster center He is not stable on most of the octahedral and tetrahedral interstitial sites in the Fe matrix near the interface. Instead He is shifted towards positions closer to the cluster. Relaxation occurs to known IVS as well as to previously unknown interfacial interstitial sites. Moreover, two or three He atoms are placed on sites found to be stable after adding a single He. The corresponding binding and incorporation energies obtained after relaxation are nearly equal to the sum of the values for the interaction with a single He atom. However, placing He dimers or trimers in the environment of a vacancy may also lead to relatively low values of the incorporation energy. Also, barriers for jumps of He atoms between interfacial sites and the center of CL clusters are determined. In the CL O-Y cluster the barriers are lower than in the CL O-Y-Ti cluster, i.e. trapping and release of He is easier in the former than in the latter. v and SIA interaction with the clusters is also attractive. The binding energy of v strongly depends on the site where v is inserted while in all studied cases the SIA is annihilated at the cluster-iron interface. Present results clearly demonstrate that the oxide-based nanoclusters are strong traps for irradiation induced defects which is in agreement with experimental findings.