Effect of Ni2O3 on diamond crystal growth in an Fe–Ni–C system under high temperature and high pressure

Abstract

Studying the influence of oxygen on the growth and properties of diamond has research significance. In this paper, we created an oxygen-rich environment by adding Ni₂O₃ to the Fe–Ni–C system. Large single crystals of oxygen-containing diamond were successfully synthesized using the temperature gradient method (TGM) in a China-type large volume cubic high-pressure apparatus (CHPA) at 5.5–6.0 GPa and 1360–1600 °C. The results show that with the increase of the Ni₂O₃ content in the Fe–Ni–C system, the rate of diamond growth decreased while the conditions for diamond growth were enhanced. The morphology of the diamonds changed from {111}, {110} and {113} mixed faces to {111} dominant face. The IR results show that the presence of Ni₂O₃ increased the nitrogen content in diamonds from 237 ppm to 543 ppm. When 3.5 wt% Ni₂O₃ was added, A-centre nitrogen began to appear in the diamonds. The XPS results confirmed that oxygen successfully entered the diamond lattice in the form of C–O, CO, O–CO and N–O with a high concentration of Ni₂O₃ additives. Meanwhile, there were no obvious impurity inclusions and cracks in the diamond crystals. In addition, the Raman peak position of the diamond appeared to red shift, and the FWHM increased from 4.93 cm⁻¹ to 5.52 cm⁻¹.