Kinetic anomalies of mixed crystal growth and their effect on the crystal isomorphic composition

Growth rate anomalies in aqueous solution growth of NaClO3 and KClO3 were first revealed by V. V. Sipyagin in 1967 and attributed to “kinetic anomalies”. These phenomena were confirmed in a series of other studies and for a variety of substances. Therefore, some universality of these anomalies was supposed that should be due to structural transformations in the liquid solutions. In this paper, we present for the first time results on growth rate oscillations found in mixed crystal growth and their impact on the isomorphic composition of solid solutions. Thick (100) Na(Cl,Br)O3 layers were grown at fixed supercooling conditions onto NaClO3 seeds in a microcrystallization cell equipped with an optical microscope. In the temperature range of 33 – 41 °C, four kinetic anomalies were found in solutions of a chlorate: bromate molar ratio of 20: 1 at supercoolings of 2.0 K and 3.0 K. Lattice parameter measurements of the grown Na(Cl,Br)O3 layers revealed a linear dependence of lattice constant vs. growth rate. By measuring Vegard's law (lattice parameter vs. solid solution composition) we were able to determine the oscillations in mixed crystal composition that accompany the kinetic anomalies in solid solution systems. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)