Nano-sized prismatic vacancy dislocation loops and vacancy clusters in tungsten

The vacancies produced in high energy collision cascades of irradiated tungsten can form vacancy clusters or prismatic vacancy dislocation loops. Moreover, vacancy loops can easily transform into planar vacancy clusters. We investigated the formation energies of these three types of vacancy defects as a function of the number of vacancies using three embedded-atom method tungsten potentials. The most favorable defect type and vacancy loop stability was determined. For very small sizes the planar vacancy cluster is more favorable than a vacancy loop, which is unstable. The void is the most stable vacancy defect up to quite large size, after that vacancy dislocation loop is more favorable. We conclude that the vacancy dislocation loops are nevertheless hlmetastable at low temperatures as the transformation to voids would need high temperature, in contrast to previous works, which found planar vacancy clusters to have lower energy than vacancy dislocation loops.