Synthesis of large diamond crystals with C3H8N4O2 as organic additive under HPHT conditions

Diamond crystals were successfully synthesized in a NiMnCo-C system by adding Malonic acid dihydrazide (C3H8N4O2) as an organic additive. The synthesized conditions in a series of experiments were about at 1300 °C–1400 °C and 6.0 GPa–7.0 GPa. The color, morphology, and inclusions of the synthetic diamond crystals were characterized by optical microscopy, Fourier transform infrared (FTIR) spectroscope and Raman spectroscope, respectively. The color of the synthesized diamonds changes from light yellow to green with increasing amounts of C3H8N4O2. The morphology of the synthesized diamonds exhibited triangular shape with abundant {111} faces. The FTIR spectra indicated that the nitrogen concentration increased whereas the hydrogen and oxygen concentration decreased with increasing concentration of the C3H8N4O2 additive. The Raman peak positions exhibited a systematic downshift with increasing amounts of C3H8N4O2 additive. According to the synthesized resultant, with increased the content of the C3H8N4O2 additive, the quality of synthesized diamond gets worse. It is interesting that the diamond content more nitrogen and less hydrogen and oxygen with increasing the C3H8N4O2 additive. By studying the effects of nitrogen, hydrogen and oxygen coexistence on the synthesis of diamond, it is would to speculate that the natural diamond nucleation and growth environment may be content more nitrogen source and less hydrogen and oxygen.