Abstract
High-quality synthetic type IIa diamond crystals of several carats, containing less than 0. 1 ppm chemical impurities and few inclusions, have been successfully synthesized by the temperature gradient method under high pressure and high temperature. The crystals are transparent over a wide range of wavelengths from ultraviolet to far infrared regions, showing no absorptions due to impurities. They also have high crystalline quality with fewer crystal defects, less internal strain, and less variation in defects among crystals than those of natural diamonds or conventional synthetic type Ib diamond. The outstanding characteristics of the synthetic type IN diamond permit application to a considerably wide range of industrial and scientific uses such as optical parts, monochromators, high-pressure anvils, and so on.
