Effects of tilting mirrors on the solid–liquid interface during floating zone growth using tilting-mirror-type infrared-heating image furnace

The effects of tilting the mirrors of a tilting-mirror-type image furnace were examined for the crystal growth of rutile by the infrared-heating floating zone (FZ) method. The mirrors were tilted from horizontal to 20° in 5° steps to examine the change of the solid–liquid interface during crystal growth. The molten zone was quenched during the FZ growth. A small amount of yttrium with an extremely small segregation coefficient was added to the molten zone so that the shape of the solid–liquid interface could be evaluated through the yttrium distribution. At zero degrees, the grown crystal side of the interface was highly convex with a convexity (h/r) of 0.55. The interface became less convex as the tilting angle increased. At the tilting angle of 20°, it was still slightly convex with h/r=0.20. On the other hand, the convexity of the interface on the feed side significantly decreased with increase in tilting angle; h/r changed from 0.50 at 0° to 0.00 at 20°, at which the interface was rather concave. A larger tilting angle stabilized the molten zone. Large rutile crystals of 18 mm diameter were successfully grown at a tilting angle of 10°.