Influence of Fe3+ and Al3+ ions on the kinetics of steps on the {1 0 0} faces of KDP

The influence of iron and aluminium impurities on the dependence of the layer growth rate versus the solution supersaturation was studied using the method of in situ interference microscopy. The dead zone of supersaturations was determined as well as the critical supersaturation value when the rate sharply increases with different impurity concentrations. Analysis of decelerating action of these impurity stoppers shows that they are firmly adsorbed by the surface and the Cabrera-Vermilyea mechanism is at work, the question of how the stopper is trapped by the crystal is still unanswered.