Abstract: In order to further meet the current demand for large-sized and high-quality sapphire materials in the current new display technology, aerospace, aviation and other fields, this paper adopts the modified Kyropoulos method and self-developed furnace to grow large-sized, high-quality sapphire crystals weighing 720 kg. Sapphire panel with diameter of 640 mm is obtained from the sapphire, and the panel has no bubbles and low-angle grain boundaries. The quality of the upper, middle and lower parts of the crystal was detected. The results show that the dislocation density of the crystal is less than 475 cm^-2, the FWHM is less than 0.004 6°, and the transmittance in the band of 400 nm to 4 000 nm is more than 83%. It shows that the micro defects in the crystal are controlled, and the crystalline properties and optical properties of the crystal are excellent.

Key words: modified kyropoulos method, sapphire crystal, optical window, dislocation, crystal growth