High-pressure synthesis of high-purity diamond crystal

Abstract

High-purity type IIa diamond crystals of weight 1–2 carats, containing less than 0.1 ppm chemical impurities and few inclusions, have been successfully synthesized by a temperature gradient method at high pressures and temperatures. The concentration of nitrogen impurities in the diamond crystals was reduced to less than 0.1 ppm by adding an element of the IVa group to the solvent as a nitrogen getter. The boron impurity concentration was reduced to less than 0.1 ppm by using a high-purity graphite (<1 ppm impurities) as the carbon source. Nickel impurities were avoided by using an Fe-Co alloy system for the solvent. Furthermore, by adding elements which can reduce the formation of carbides such as TiC or ZrC in the solvent, inclusions of the carbide or the solvent metal in the diamond crystal were substantially decreased, and consequently good-quality type IIa diamond crystals were obtained even at a growth rate as high as 2–3 mg h −1.