Barannik S. The influence of the non-stationary growth conditions on the formation of impurity striation in sapphire

The behavior of crystallization front of binary melt has been studied within the framework of non-stationary one-dimensional model at subcritical regime under temperature profile (TP) movement along crystal-melt system with constant velocity, constant acceleration and the velocity altering by sinusoid manner. It has been revealed that crystallization rate behaves non-monotonously under primary transition process at TP constant velocity exceeding the velocity at which the zone of concentration overcooling appears in the melt. Under variable velocity of TP movement and at distribution coefficient of the impurity k < 1 the average by time of impurity concentration at inter-phase boundary is less and at k > 1 is more than at constant velocity. So, under variable velocity of TP the effect analogous to partial mixing of the melt is developing. It has been experimentally shown that under constant rate of sapphire elongation by horizontal directed crystallization method at subcritical regime the crystallization rate carries out periodical oscillations synchronized with formation of impurity bands in the crystal. On the base of obtained data the method of crystal growth allowing the optimization of sapphire growth process without impurity bands has been developed.