Abstract: Diamond single crystals were synthesized in Ni70 Mn25 Co5-graphite-sulfur powder system under the conditions of 5.5-5.7 Gpa and 1450-1550 ℃.They were composed of equally developed {111} and {100} faces, with a little inclusions in them.And there were usually several depressions on the crystal, in which there were usually a lot of small pits, and a smaller adjunct crystal connecting with the main crystal.It was shown by the wavelength dispersive X-ray fluorescence spectrum that with the increase of the sulfur content, the contents of manganese and sulfur in the crystal obviously increased, while that of nickel and cobalt tended to decrease.This was attributed to the interaction between manganese and sulfur which had changed the catalystal characteristcs of the NiMnCo alloy by changing its composition stoichiometry.

Key words: Diamond single crystals were synthesized in Ni70 Mn25 Co5-graphite-sulfur powder system under the conditions of 5.5-5.7 Gpa and 1450-1550 ℃.They were composed of equally developed {111} and {100} faces, with a little inclusions in them.And there were usually several depressions on the crystal, in which there were usually a lot of small pits, and a smaller adjunct crystal connecting with the main crystal.It was shown by the wavelength dispersive X-ray fluorescence spectrum that with the increase of the sulfur content, the contents of manganese and sulfur in the crystal obviously increased, while that of nickel and cobalt tended to decrease.This was attributed to the interaction between manganese and sulfur which had changed the catalystal characteristcs of the NiMnCo alloy by changing its composition stoichiometry.