Abstract
This review, for the first time, summarizes the results of studies of the defect formation mechanisms in mixed crystals grown from aqueous solutions. The general mechanism of interaction of a crystal with a foreign solution is described (reaction of isomorphous replacement). As a result of this reaction, the crystal surface turns into a mosaic of local areas where multidirectional processes (dissolution and growth) occur simultaneously. Data on mosaic microinhomogeneity, which is a new type of composition inhomogeneity inherent solely to multicomponent crystals, is presented. A new mechanism for the mismatch stress relaxation in heterocompositions of brittle crystals grown from low-temperature solutions is described; in this case, the formation of misfit dislocations is impossible and stress relaxation occurs due to the formation of numerous inclusions at the interface. The general concept of growing high-quality mixed crystals from solutions is described, using the example of K2(Co, Ni)(SO)2 · 6H2O (KCNSH) mixed crystals.
Highlights
The phrase mixed crystals here describes substitutional solid solutions of isomorphous components.The possibility of growing crystals of solid solutions is of prime importance for creating materials with specific properties
Our recent study [21] of KCNSH mixed crystals grown from solutions with a mass ratio of the isomorphic components KCSH:KNSH = 1:2 has shown a clear dependence of the value of micromosaic
Our recent study [21] of KCNSH mixed crystals grown from solutions with a mass ratio of the isomorphic components KCSH:KNSH = 1:2 has shown a clear dependence of the value of micromosaic Ni inhomogeneity |δcNi| on the solution supercooling ΔT (Figure 8)
Summary
The phrase mixed crystals here describes substitutional solid solutions of isomorphous components. The possibility of growing crystals of solid solutions is of prime importance for creating materials with specific properties. Due to the huge number of defects in mixed crystals, there have not yet been any examples of their practical use. According to the Gibbs phase rule, a three-component system consisting of a solvent (water) and two salts has two degrees of freedom (temperature and composition) at constant pressure. This means that, at a given temperature, there is a continuous series of saturated solutions and the same number of crystals, the compositions of which correspond to the equilibrium conditions with these solutions.
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