86 3 Formation of Mixed Crystals in Solutions
(Laemmlein 1948, 1973). Heterogeneity of the crystals produced can be classified
as follows: sectorial heterogeneity formed owing to differences in adsorption prop-
erties of various crystal faces; zonal heterogeneity caused by alterations in growth
rate; and structural heterogeneity caused by concentration changes in imperfect
regions of a crystal. Selection of admixtures proceeds at the atomic level and
depends upon the admixture solubility (the Ruff rule: Chernov 1984) and solubility
of surface compounds formed by the admixture (the Panet rule: Laemmlein 1948,
1973). The process has statistical nature regulated by difference in characters of the
bonds formed by the crystal’s own constituents and the admixture particles that
results in development of local deformations and changing in elastic energy of the
crystal lattice. The concepts developed to elucidate the growth mechanisms of
mixed crystals, as well as use of elements of external and internal crystal morphol-
ogy (faceting, details of the surface relief, inclusions, and other defects) for genetic
examinations of mixed crystals, do not principally differ from a similar studies of
crystals having constant compositions.
As stated in Chapter 1 (Sects. 1.1, 1.2, 1.4, and 1.5), in 1983 we discovered
(optical microscope resolution) nontrivial phenomena of isomorphic exchange
between a crystal and solution and developed a first model of monocrystal iso-
morphic substitution comprising synchronized processes of crystal dissolution
and growth (Glikin and Sinai 1983). Next, the place for this process among the
variety of exchange reactions was determined (Glikin and Sinai 1991). Later, the
proposed mechanism was proved by quantitative physicochemical results (Glikin
et al. 1994), and, then, we formulated a conceptual physicochemical basis com-
bining regularities of isothermal substitution, growth, and heterogeneous metast-
able equilibria in supercooled solutions (Glikin 1995, 1996a). During the last
decade this model was elaborated to incorporate the results of detailed optical-
microscopic and kinetic researches (Kryuchkova et al. 2002; Glikin et al. 2003)
and data obtained by means of several high-resolution methods including X-ray
topography (Glikin et al. 2003), electron microscopy (Putnis et al. 2001; Putnis
2002), and atomic-force microscopy (Voloshin et al. 2004; Woensdregt and
Glikin 2005).
These findings comprising incorporation of impurities into a crystal; formation
of autoepitaxial excrescences; influence of the component solubilities and volume
effect of substitution upon these phenomena; correlations between replacement,
growth, and dissolution; heterogeneous metastable equilibria; and other parameters
partially discussed in Chapter 1 appeared to be far beyond the boundaries of tradi-
tional interpretations developed for growth of crystals having constant composi-
tions and co-crystallization of isomorphic substances (Melikhov and Merkulova
1975; Chernov 1984). Analysis of capturing individual atoms appears to be insuf-
ficient for interpretations, as it is capable of clarifying neither mechanism of infor-
mation transaction between different sites of the crystal defining the contents of
individual components, nor the feedbacks regulating these contents in accordance
with the growth conditions. Physicochemical analysis of formation of a mixed
crystal considered as an integral entity of interrelated isomorphic components may