Synthesis of diamond with the highest nitrogen concentration

Nitrogen concentrations in diamond grown from non-metallic solvent-catalysts such as Na2CO3 and Na2SO4 have been measured using infrared absorption microscopy. It was found that 1200 to 1900 atomic ppm of nitrogen atoms are incorporated in the crystals when a sample container made of boron nitride was used, although a few hundred ppm of nitrogen were present when an NaCl container was used instead of BN. Such high concentrations of nitrogen have not been found in synthetic diamonds when conventional metallic solvent-catalysts are used. The result of this study is consistent with the inference that natural diamond, in which high concentrations of nitrogen are usually present, grew from molten rocks, i.e., non-metallic catalysts. (C) 1999 Elsevier Science S.A. All rights reserved.