Morphology transitions during the growth of alkali halides from solution

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Four alkali-halide salt compounds were prepared by the evaporation of aqueous solutions on mica substrates. Growth runs were carried out over a wide range of conditions by varying the substrate temperature and the evaporation rate independently. During RbI growth, where the misfit between salt and mica lattices is small, the morphology of the deposited salt crystals tends to be faceted, except under extreme conditions. For salts with a larger misfit relative to the substrate (KI, RbBr, and CsBr), faceted growth is no longer the most common form. Despite the differences among the various compounds, in all cases we find sets of growth conditions which can favor faceted, dendritic, directional-array, and seaweed morphologies. While many previous experiments have focused upon a single morphology transition, these experiments show that at least four distinct morphologies can be produced in a single material system when growth conditions are varied sufficiently.