Formation of Mixture of A and C Centres in Diamond Synthesized with Fe₉₀Ni₁₀-C-High-Content Additive NaN₃ by HPHT

Very rich nitrogen concentration with the dominant C centres and some A centres are found in diamonds grown from a Fe₉₀Ni₁₀-C-high-content NaN₃ additive system. The concentrations of C centres rapidly increase with increasing content of NaN₃ additive, while the concentrations of A centres increase slowly. The total nitrogen concentration tends to increase rapidly
with increasing content of NaN₃ additive when the content of NaN₃ is below 0.7wt%. However, the total concentration of nitrogen in the diamonds increases slowly when the content of NaN₃ is further increased up to 1.0wt%, and the total nitrogen average concentration are calculated to be around 2230ppm for most of the analysed synthetic diamonds. Furthermore, the nitrogen impurities in different crystal sectors of the diamonds are inhomogeneously distributed. The nitrogen impurities in the diamonds in 111 zones are incorporated more easily than that in 100.