Abstract:The work was based on the relationship between the crystal structure and parameters of diamonds in the synthetic process, in which Ni-Mn-C powder catalyst was used. At first, the diamond crystals nucleated in a cubic-octahedron morphology through controlling such synthetic parameters as temperature and pressure in a parameter region where cubic-octahedron ctystals can be obtained. Then the diamond nuclei grew epitaxially into crystals with a perfect octahedron morphology through increasing the synthesis temperature and decreasing the synthesis pressure in a parameter region where octahedron crystals can be obtained.

Key words: high grade; diamond;eqitaxial growth