By the second half of the twentieth century, a new branch of materials
science had come into being -- crystalline materials research. Its
appearance is linked to the emergence of advanced technologies primarily
based on single crystals (bulk crystals and films). At the turn of the
last century, the impending onset of the "ceramic era" was forecasted.
It was believed that ceramics would play a role comparable to that of
the Stone or Bronze Ages in the history of civilization. Naturally, such
an assumption was hypothetical, but it showed that ceramic materials had
evoked keen interest among researchers. Although sapphire traditionally
has been considered a gem, it has developed into a material typical of
the "ceramic era." Widening the field of sapphire application
necessitated essential improvement of its homogeneity and working
characteristics and extension of the range of sapphire products,
especially those with stipulated properties including a preset
structural defect distribution. In the early 1980s, successful
attainment of crystals with predetermined char- teristics was attributed
to proper choice of the growth method. At present, in view of the fact
that the requirements for crystalline products have become more str-
gent, such an approach tends to be insufficient. It is clear that one
must take into account the physical-chemical processes that take place
during the formation of the real crystal structure, i.e., the growth
mechanisms and the nature and causes of crystal imperfections.
