The diamond growth from Li₂CO₃, Na₂CO₃, K₂CO₃ and Cs₂CO₃ solvent-catalysts at P=7 GPa and T=1700-1750°C

In the series of experiments at P=7GPa and T=1700-1750°C with their duration from 10min to 18.5h the processes of diamond spontaneous nucleation and growth on a seeds in the systems Li₂CO₃-C, Na₂CO₃-C, K₂CO₃-C and Cs₂CO₃-C were studied using the 'split-sphere' type of apparatus (BARS). Diamond formation in such conditions requires more time than in metal-graphite systems. The essential dependence of diamond morphology and nucleation peculiarities on the composition of crystallization medium was established. It is shown that the catalytic activity of alkaline carbonates is determined by the sequence Li₂CO₃≫Na₂CO₃>K ₂CO₃>Cs₂CO₃, while the morphology of diamond crystals, synthesized in the carbonates of the sequence, changes regularly from cuboctahedron to octahedron. The maximum size of synthesized crystals reaches 600-700μm, while the maximum layer, grown on a seed is 400-500μm. The rate of synthesis reaction and the number of diamond nuclei decrease regularly with the increase of cation radius in the sequence Li⁺→Na⁺→K⁺→Cs⁺, while the duration of the synthesis inductive period increases simultaneously.