Growth of Sapphire Disks from the Melt by a Gradient Furnace Technique

Abstract : Single crystal Al2O3 (sapphire) is a candidate material for various window applications. A gradient furnace technique has been developed for the growth of large sapphire disks, 7.3 cm in diameter and 1.5 cm thick, from the melt in molybdenum crucibles. The disks are free of gas bubbles and inclusions and consist of several large pie-shaped grains. Within the grains dislocation densities of 100,000/sq.cm. have been measured. The disks are essentially transparent to radiation from wavelengths of 0.25 micrometers in the ultraviolet spectrum to 4.5 micrometers in the infrared spectrum.