Spontaneous mixing of binary alkali halide crystal by successive evaporation

Experimental studies on the mixing of alkali halide clusters of 200 nm sizes were performed systematically by the successive evaporation of different alkali halides on carbon substrates. The alkali halides used were NaCl, NaBr, KCl, KBr, KI, RbCl, RbBr, CsCl and CsBr. Intermixing took place independent of the crystal structure. It became evident that the limit of mixing was governed by the ratio of ionic radii. If the ratio of ionic radii between the cation and/or anion was more than 68%, intermixing occurred. It was also found that the crystal structure formed by intermixing between NaCl-type and CsCl-type structures becomes the NaCl type. If four different elements of cations and anions are involved, two mixture phases grew. The key elements of mixing were the nearest ionic radii.