Short-term high-temperature annealing of ZnS crystals in a zinc atmosphere was shown to cause rapid Zn diffusion through dislocation pipes along growth-dislocation lines. As a result, the impurity ions of divalent chromium localized in Cottrell atmospheres outside Read cylinders became singly ionized. Plastic deformation of such ZnS crystals or the passing of an electric current through them under a voltage higher than a certain threshold value leads to a decrease in the number of univalent chromium ions. This decrease could be explained by an increase in the radius of Read cylinders as growth dislocations leave Cottrell atmospheres and by an increase in the linear density of their electric charge.

EPR Studies of Changes in the Charge State of Cr over a Cross-Section of Dislocation Pipes in ZnS Crystals. S.A.Omelchenko, A.A.Gorban, M.F.Bulanyĭ, A.A.Timofeev: Physics of the Solid State, 2006, 48[5], 882-6