HIGH-PRESSURE SYNTHESIS OF HIGH-PURITY DIAMOND CRYSTAL

High-purity type IIa diamond crystals of weight 1-2 carats, containing less than 0.1 ppm chemical impurities and few inclusions, have been s uccessfully synthesized by a temperature gradient method at high press ures and temperatures. The concentration of nitrogen impurities in the diamond crystals was reduced to less than 0.1 ppm by adding an elemen t of the IVa group to the solvent as a nitrogen getter. The boron impu rity concentration was reduced to less than 0.1 ppm by using a high-pu rity graphite (<1 ppm impurities) as the carbon source. Nickel impurit ies were avoided by using an Fe-Co alloy system for the solvent. Furth ermore, by adding elements which can reduce the formation of carbides such as TiC or ZrC in the solvent, inclusions of the carbide or the so lvent metal in the diamond crystal were substantially decreased, and c onsequently good-quality type IIa diamond crystals were obtained even at a growth rate as high as 2-3 mg h(-1).