The kinetics of defect aggregation and metal colloid formation in ionic solids under irradiation

Results of a microscopic theory describing diffusion-controlled aggregation of radiation Frenkel defects - F and H centers - are discussed. We suggest interpretation of experimental data on metal colloid formation in the two ionic solids with different crystalline structures - LiF and CaF₂ - observed under electron irradiation with subsequent heating. Theory successfully reproduces the main experimental observations including Ostwald ripening of small colloids into large colloids in the narrow temperature interval and suggests that radiation-enhanced F center diffusion occurs in CaF₂ with as low activation energy as 0.4 eV. In contrast, the activation energy for a single F center diffusion in LiF is found to be as high as 1.5 eV. The key role of mutual defect elastic attraction in their aggregation is demonstrated.