Mixed type Ib-IIa diamond from a Fe-Mg2Si3O8.5H2O-C system under high pressure and high temperature

The composition of the crystalline medium has an essential effect on the formation and properties of diamonds. Large single-crystal diamonds grown in a Fe-Mg2Si3O8.5H2O-C system by the temperature gradient method (TGM) at 5.8-6.3 GPa and 1400-1480 degrees C were investigated. It was found that as the Mg2Si3O8.5H2O content increased from 0 to 4 wt%, the synthesis pressure and temperature both increased, and more nitrogen-vacancy (NV) defect centers appeared in the diamond crystal. The nitrogen impurity concentration in type Ib diamonds synthesized in the pure Fe-C system was about 90 ppm, and the distribution of nitrogen impurities was uniform from core to rim. Furthermore, with a Mg2Si3O8.5H2O content of approximately 4.0 wt%, type Ib-IIa diamond was successfully synthesized. The infrared spectra (IR) results showed that the nitrogen content of the type Ib-IIa diamond was higher in the central zone of the crystal (79 ppm), decreased in the intermediate zone (42 ppm), and decreased further at the periphery (< 1 ppm). Thus, the type Ib-IIa diamond had significant heterogeneity in the distribution of nitrogen.

Automated summary

The composition of the crystalline medium affects the formation and properties of diamonds. Increasing the Mg2Si3O8.5H2O content led to higher synthesis pressure and temperature, as well as more nitrogen-vacancy defect centers in the diamond crystal. Type Ib diamonds had uniform nitrogen impurity distribution, while type Ib-IIa diamonds showed significant heterogeneity in nitrogen distribution.