The substitutional fraction ($f_s$) of 0.1 at.?Ce in vanadium depends on the lattice temperature during implantation and is 0.73, 0.73, and 0.15 at 5, 77, and 300 K, respectively. Increasing the implanted Ce concentration at 300 K to 3.3 at. ?eads to an increase of $f_s$ from 0.15 to 0.66. Postirradiation of VCe systems as produced at 300 K with He ions at 77 K leads to an increase of $f_s$. If the postirradiated systems are warmed up to room temperature $f_s$ decreases. It is concluded that Ce-vacancy clusters are formed within the prompt cascade regime and by trapping mobile vacancies. Pre- and postimplantation experiments proved that the increase of $f_s$ with Ce concentration is due to cluster dissolution accompanied by the formation of competing vacancy-trapping centers.

• Received 28 January 1986

DOI:https://doi.org/10.1103/PhysRevB.34.5