Abstract :
Using a fast multi-window NMR technique, we have measured in-situ the mean jump width x of mobile dislocations during plastic deformation in a series of NaCl single crystals with varying Ca++ content. Aside from immobile forest dislocations, the Ca++ impurities form additional obstacles for the moving dislocations thus lowering x. We found that the Ca++-related obstacles exhibit a pronounced non-random distribution which results in a corresponding broad distribution of x. We show that the data can be evaluated by means of an appropriate distribution function g(1/x) with an uncommon dependence of the observed fitting parameters on the Ca++ content. As expected, quenching of a sample leads to a more uniform distribution of the Ca++-related obstacles resulting in a corresponding narrowing of g(1/x).
