Growth of the {101} face of KDP crystals in the presence of dye Chicago Sky Blue
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Growth of the {101} face of KDP crystals in the presence of dye Chicago Sky Blue Olga A. Gliko, Natalia P. Zaitseva*, Leonid N. Rashkovich Department of Physics, Moscow State University, Moscow 119899, Russia *Lawrence Livermore National Laboratory, Livermore, CA 94550, USA ABSTRACT In situ interference technique is used for a study of morphology and growth kinetics of a pyramidal face of KDP crystals with dye Chicago Sky Blue. It is shown that the impurity is captured by a crystal when its concentration in the solution exceeds a certain temperature depended value. In the presence of impurity the face loses its stability with increasing of supersaturation. Further increase of supersaturation leads to the restore and subsequent loss of stability. The experimental results are interpreted in the framework of earlier developed model for a crystal growth in the presence of the easily desorbed mobile impurity. The parameters characterizing the adsorption behavior of mobile impurity and its capture have been determined. INTRODUCTION It is known that the impurities strongly affect the structural perfection of the crystals grown from the solution. However, the mechanisms of the impurity influence are not studied experimentally well in spite of numerous theoretical works on this subject. Recently, the number of papers dealing with the growth of KDP crystal in the presence of different impurities was published [1-5]. It was found that the most of cationic impurities affected only the growth of prismatic face, and did not influence the growth of a pyramidal face. For example, the difference in the values of distribution coefficient between solution and growth sectors of these faces for ions of the iron-group exceeds one hundred times. Probably, this fact is due to the positive charge of the face of a pyramid and neutrality of a prismatic face [6]. The anionic impurities have a weak effect on the KDP growth, but some of them slow down the growth of pyramid [4]. However, it was found that the dye Chicago Sky Blue enters the growth sectors of the pyramidal face and intensively stains them [7]. At the same time, the dye is not captured by the prismatic faces. The formula of dye is C34H24N6Na4O16S4 - 1-amino-8-naphthol2,4–disulfonic acid, F.W. = 992.82, and it has 4 negatively charged groups SO3- in the solution. These experiments were performed at room temperature with the solutions containing a large amount of the dye by the use of spontaneous crystallization technique. The crystal size did not exceed several millimeters. Some features of incorporation of the dye in the crystal were determined for the large KDP crystals with the linear sizes more than 10 cm grown using the temperature decreasing technique [8]. Nevertheless, it was interesting to study the influence of a given impurity on the KDP crystallization in more detail, because no data on the effect of impurity on the morphology and growth kinetics of the pyramidal face were reported up to now. TECHNIQUE The in situ interference technique was used [9]. The crystal plate (~5
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