Kinetic peculiarities of diamond crystallization in K–Na–Mg–Ca–Carbonate-Carbon melt-solution

The kinetic peculiarities of diamond crystallization in multicomponent K–Na–Mg–Ca–carbonate-carbon system have been studied in conditions of diamond stability at 1500–1800$^\circ$C and 7.5–8.5 GPa. It has been established that the diamond phase nucleation density at a fixed temperature of 1600$^\circ$C decreases from 1.3 $\times$ 10$^5$ nuclei/mm$^3$ at 8.5 GPa to 3.7 $\times$ 10$^3$ nuclei/mm$^3$ at 7.5 GPa. The fluorescence spectra of obtained diamond crystals contain peaks at 504 nm ($H$3-defect), 575 nm (NV-center), and 638 nm (NV-defect), caused by the presence of nitrogen impurity. In the cathodoluminescence spectra, an $A$-band with the maximum at 470 nm is present. The obtained data make it possible to assign the synthesized diamonds in the carbonate-carbon system to the mixed Ia + Ib type.