Positron Annihilation Study of Vacancy Clusters in Ni with Dislocation Lines

Although the positron lifetime depends on the defect status in the solids, many features on the intermediate lifetime between matrix and a single vacancy are left unknown in various crystals. One example of such defects is a collapsed type vacancy cluster like a stacking fault tetrahedron (SFT), and in the present study attempts have been performed to clarify these aspects in Ni. Positron lifetime calculations were carried out for various SFTs obtained in model Ni lattice through complete relaxation process. Shorter lifetimes (130psec-150psec) than a single vacancy was obtained for the SFTs which have larger sizes than V15. In these SFTs which have larger sizes than V15. In these SFTs the positron trapping occurs at four corners of SFTs and positrons are not trapped at six stair-rod dislocations. Comparison with the experimental result obtained after low temperature electron irradiation for Ni and deformed Ni was made and a good agreement was obtained