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In this paper, we explore diamond synthesis with a series of experiments using an Fe-Ni catalyst and a P3N5 additive in the temperature range of 1250-1550 0C and the pressure range of 5.0-6.3 GPa. We also investigate the influence of nitrogen on diamond crystallization. Our results show that the synthesis conditions (temperature and pressure) increase with the amount of P3N5 additive increasing. The nitrogen impurity can significantly influence the diamond morphology. The diamonds stably grow into strip and lamellar shapes in the nitrogen-rich environment. The Fourier-transform infrared spectrum shows that the nitrogen concentration increases rapidly with the content of P3N5 additive increasing. By spectrum analysis, we find that with the increase of the nitrogen concentration, the Ib-type nitrogen atoms can aggregate in the A-centre form. The highest A-centre nitrogen concentration is approximately 840 ppm. [ABSTRACT FROM AUTHOR]

A series of diamond crystals doped with hydrogen is successfully synthesized using LiH as the hydrogen source in a catalyst-carbon system at a pressure of 6.0 GPa and temperature ranging from 1255 ° to 1350 °. It is shown that the high temperature plays a key role in the incorporation of hydrogen atoms during diamond crystallization. Fourier transform infrared micro-spectroscopy reveals that most of the hydrogen atoms in the synthesized diamond are incorporated into the crystal structure as sp3 -CH2-symmetric (2850 cm-1) and sp3 CH2-antisymmetric vibrations (2920 cm-1). The intensities of these peaks increase gradually with an increase in the content of the hydrogen source in the catalyst. The incorporation of hydrogen impurity leads to a significant shift towards higher frequencies of the Raman peak from 1332.06 cm-1 to 1333.05 cm-1 and gives rise to some compressive stress in the diamond crystal lattice. Furthermore, hydrogen to carbon bonds are evident in the annealed diamond, indicating that the bonds that remain throughout the annealing process and the vibration frequencies centred at 2850 and 2920 cm-1 have no observable shift. Therefore, we suggest that the sp3 C-H bond is rather stable in diamond crystals. [ABSTRACT FROM AUTHOR]