The effect of adding Cu on the nitrogen removal efficiency of Ti for the synthesis of a large type IIa diamond under high temperature and high pressure

Abstract

Large single crystal diamonds were synthesized using Ti/TiC and Cu as additives in the Fe64Ni36-C system under 5.6 GPa and at 1543 K. The synthesized crystals were characterized by optical microscopy and infrared spectroscopy. Results show that both Ti and TiC react with N to form TiN and Ti (C1-x, Nx), respectively, which leads to a poor nitrogen removal efficiency and a large number of inclusions and pits in the crystals. Co-doping TiorTiC with Cu promotes the decomposition of TiC to release Ti, which improves the nitrogen removal efficiency, and thereby reduces the number of defects and inclusions in the diamond crystals. A high-quality type IIa diamond crystal was optimally synthesized when the Ti/Cu contents were 1.70 wt.%/1.06 wt.% (Ti: Cu = 4: 2.5).