Scale-up of the Heat Exchanger Method to Grow 14.5Inch Diameter Sapphire Boule for IR Dome.

摘要

Sapphire crystals 14-1/2-inch diameter were successfully solidified out to the crucible, but the crystals were cracked. The heat flow conditions were sufficient to maintain and drive a planar solidification front. This was surprising, since the crucible was less than 1-1/2 inches from the heating element at its closest point. ' Cracking in all runs occurred due to a breakdown of crystallinity. One grain was nucleated a short distance from the seed in the first two boules. The breakdown in crystallinity near the seed appears to be related to sagging of the crucible. Cracking, the only problem, was due to breakdown in crystallinity. This was traced to the sagging of the crucible causing uneven temperature distribution along the bottom. (Author)