Computer Simulations of I‐Center Annealing in KCl and KBr Crystals. Theoretical Interpretation of Thermostimulated Experiments

Results of computer simulations of the kinetics of correlated annealing of pairs of close α–I and F–I centers in KCI and KBr crystals, enhanced by I‐center diffusion and Coulomb or elastic attractions, respectively, are presented. Special attention is paid to the conditions under which multi‐stage annealing stages arise as it has been observed experimentally more than once. Our general conclusions are: (i) a weak elastic interaction affects the recombination kinetics and the survival probability even for relatively well‐separated F–I pairs, the more so is true for the case of Coulomb attraction between charged α–I pairs; (ii) the multi‐step (kink) structure arises only for close (typically, up to fourth‐nearest neighbour) defects. To explain the strongly separated stages observed experimentally for α–I (17 to 21 K, 30 to 39 K in KCI and 18 to 22 K and 27 to 30 K in KBr) a very particular initial distribution of defects is required consisting of two groups of close and well‐separated defects. It gives strong support to the results of recent computer simulations that an interstitial ion created due to electron trapping by an H center can be transformed into a crowdion which could be displaced athermally by a long distance from a vacancy (five to seven interionic distances).