Nitrogen concentration control in diamonds grown in Co-(Fe)-Ti/Al solvents under high-pressure and high-temperature

A systematic study for the continuous control of nitrogen concentrations in synthetic diamonds ranging from 100 to 0.1 ppm is conducted. Nitrogen concentrations in diamonds grown under high-pressure and high-temperature were controlled at ppm levels by adding Ti/Al in Co and Fe-Co alloy solvents. In the Co solvents, the nitrogen concentrations decreased exponentially from 100 to 0.2 ppm for Ti additions and to 40 ppm for Al additions. The nitrogen gettering efficiency increased in the order of Co-Al, Co-Ti, and Fe-Co-Ti solvents. Thus, the Co-Ti solvents were preferable for tuning the nitrogen concentration (>0.2 ppm), whereas the Fe-Co-Ti solvents were promising for obtaining a minimum nitrogen concentration (<0.2 ppm). These features may be attributed to the known nitrogen gettering efficiency differences between Fe and Co as well as Ti and Al.