The dynamics of F-center (an O vacancy which had trapped 2 electrons) aggregation in thermochemically reduced MgO single crystals with an exceptionally high F-center concentration (6 x 1018/cm3) were examined. A theory of the Mg nano-cavity formation process was developed based on diffusion-controlled aggregation of elastically interacting F centers and their annihilation at traps. It was shown that in contrast to the generally accepted viewpoint, the F centers in the bulk were not annealed out at the external sample surface but at internal defects, such as dislocations, sub-grain boundaries and impurities. The mutual attraction of the F centers was a key factor controlling the aggregation process.

Diffusion-Controlled Annihilation and Aggregation of F-Centers in Thermochemically Reduced MgO Crystals. E.A.Kotomin, V.N.Kuzovkov, A.I.Popov, M.A.Monge, R.González, Y.Chen: Nuclear Instruments and Methods in Physics Research Section B, 2002, 191[1-4], 208-11