On the nature of supersaturation barriers observed during the growth of crystals from aqueous solutions containing impurities

• Published in: Journal of crystal growth 2002-07, Vol.242 (1), p.215-228
• Main Author: Sangwal, K.
• Format: Article
• Language: English
• Subjects: A1. Adsorption; A1. Growth models; A1. Impurities; A1. Surface processes; A2. Growth from solutions; B1. Ammonium oxalate monohydrate; B1. Potassium dihydrogen phosphate; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from solutions; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/S0022-0248(02)01326-X

The nature of supersaturation barriers observed during the growth of single crystals from aqueous solutions containing impurities is investigated using theoretical and empirical expressions relating the face growth rate and step velocity with supersaturation. For the analysis, the experimental data of the supersaturation dependence of growth rate of the (1 0 0) face of ammonium oxalate monohydrate (AO) crystals and step velocity of the (1 0 0) face of potassium dihydrogen phosphate (KDP) crystals growing from aqueous solutions containing trivalent metal chloride impurities at a constant temperature and predefined supersaturations were used. It was found that: (1) at relatively low supersaturations the model involving a complex source of cooperating screw dislocations and the power-law approach predict the same values of supersaturation barrier while an empirical parabolic relation predicts somewhat lower values of supersaturation barrier than the other models, (2) the origin of two supersaturation barriers for the step velocity during the growth of KDP crystals is associated with instantaneous and time-dependent adsorption of the impurity on the growing surface, (3) the dependence of supersaturation barriers on impurity concentration follows Freundlich and Langmuir adsorption isotherms during the growth of AO and KDP crystals, respectively, and (4) Kubota–Mullin's mechanism of adsorption of impurities at kinks in the ledges holds in the case of growth of AO and KDP crystals in the presence of trivalent cations.