Structure and hardness of octahedral natural diamond single crystals depending on the HPHT treatment conditions

The structure evolution of octahedral natural diamond single crystals has been studied depend� ing on the HPHT treatment using Raman scattering and infrared spectroscopy. It has been found that the format ion of a polycrystalline diamond capsule around a single crystal at p = 8 GPa and T = 1500°C gives rise to a combined structuralstressed state in the single crystal due to its plastic strain. This state has been manifested by a significantly (more than double) broadening of the characteristic line of diamond (1332 cm -1 ) in the Raman spectrum and the increase of a single crystal hardness from 105 to 120 GPa.