FLOATING-ZONE CRYSTAL-GROWTH WITH A HEATED AND IMMERSED SHAPER - EXPERIMENTS

The conventional floating-zone crystal growth process was modified such that a shaper in the form of a step is heated and immersed in the melt zone during growth. This modified process was studied using NaNO3 as a model material. Single crystals were grown from 6 mm diameter cast rods of NaNO3. It was demonstrated that crystals with a very uniform diameter and smooth surface can be grown by this modified process. The effect of the temperature and travel speed of the step was examined. Some problems encountered during crystal growth and their corrections were described, i.e., gas porosity, crystal cracking, melt creeping and crystal wandering. It was found that the heated step helped prevent melt creeping and crystal wandering. For comparison crystal growth was also carried out using an immersed sheet heater.