Probable convections in Czochralski crucibles are reviewed. Combined free and forced convection due to crystal rotation is analyzed in detail. The convection in the melt can be grouped into two classes: free convection dominance and forced convection dominance. Temperature field slightly depends on the convection in the melt with a low Prandtl number and is essentially determined by conduction. However, it depends on the convection for high Prandtl number melts and the interface shape is convex toward the melt if free convection is dominant and concave if forced convection is dominant. The abrupt change of the interface shape from convex to concave during the growth of some garnets is due to the fluid flow transition from free convection to forced convection. Two kinds of crystal shape instability are possible for high Prandtl number melts with a high Biot number. The effect of the crucible rotation on the convection in the melt is also examined.
The purpose of this report is (1) to show the relationship among the dislocation generation and growth conditions in the Czochralski grown KCl crystals and (2) to elucidate the mechanism of dislocation generation during growth. The following growth factors were examined; (i) temperature gradient, (ii) growth rate, (iii) crystal rotation rate, (iv) crystal diameter and (v) impurity doping Furthermore, the effect of the cyclic annealing upon the reduction of the dislocation density was also examined. Dislocations in KCl crystals are much easier to multiply than those in covalent crystals and metals owing to the following reasons; (i) the highly stress sensitive dislocation mobility, (ii) the high thermal expansion coefficient, (iii) the low thermal conductivity, and hence special attention has been paid to the effect of the thermal stresses in this work.