Effects of the diameter of rutile (TiO2) single crystals grown using tilting-mirror-type infrared heating image furnace on solid–liquid interface and etch pit density

The effects of the diameter of a rutile (TiO2) crystal on interface shape during TiO2 crystal growth by the floating zone (FZ) method using a tilting-mirror-type image furnace and on the etch pit density (EPD) of rutile single crystals were examined. To investigate the diameter effect on the interface shape, the grown crystal diameter was varied from 6 to 11 mm at two different tilting angles (θ) of 0° and 20°, respectively. The interface shape was characterized by the convexity (h/r) of interface, where h and r represent the height of the interface and the radius of the grown crystals. The h/r of the crystal–melt interface decreased from 0.15 to 0.0 with an increase in the crystal diameter from 6.5 to 11.2 mm at θ=20°, whereas it increased from 0.45 to 0.58 with an increase in the crystal diameter from 6.0 to 11.0 mm at θ=0°. This result suggests that the molten zone becomes stable at θ=20° for the growth of crystals with a larger diameter. To investigate the crystal diameter effect on the EPD, rutile single crystals with diameters of 10, 16 and 19 mm were grown at θ=20°. The EPDs at the center were 1.0−1.4×104 cm−2, which were much smaller than those at the periphery, i.e., 8.0−13.0×104 cm−2, for all the grown crystals with different diameters.