GROWTH DEFECTS IN YTTRIUM SCANDIUM GALLIUM GARNET SINGLE-CRYSTALS

The crystal structure of a garnet is distinguished by a cubic unit cel l containing eight formula units {A3}[B2](C3)O12, where the curly brac kets, square brackets, and the parentheses respectively designate the cation sites in the dodecahedral, octahedral, and tetrahedral coordina tions with respect to oxygen. For materials with such a structure in g eneral and, particularly, for yttrium-scandium-gallium garnet (YSGG) o f the composition {Y3-xSex}[SeyGa2-y]Ga3O12, the difficulties in prepa ring single crystals with given concentration and equilibrium distribu tion of the basic components along the length and the transverse cross section are caused for three main reasons: their unique crystal struc ture (the existence of three crystallographic sites for the cations) a nd specific properties of the Se atoms (the possibility of its distrib ution over two or even all the three crystallographic sites); features of their phase diagrams (the composition of the crystal corresponds t o the composition of the melt only in the case of the congruently melt ing compounds and is different in all the other cases); and substantia l influence on the uniformity of the composition of the growing crysta ls by the technological features of their preparation (the shape of th e crystallization front), presence of growth defects such as, e.g., th e 'faceting effect' and the growth striations. This work is devoted to a study of the defect formation in the YSGG single crystals grown by the Czochralski method.