Diamond Growth from a Phosphorus-Carbon System at High Pressure High Temperature Conditions

Diamond crystallization in phosphorus-carbon systems was studied at high pressures and high temperatures of 6.3 and 7.5 GPa and 1400-1850 degrees C. To allow for the crystallization kinetics, the run times were set as long as 40-60 h. As a result, the range of the pressure-temperature (P-T) conditions of diamond nucleation and growth on seeds was considerably extended and the fields of diamond spontaneous nucleation, diamond growth on seeds, and formation of metastable graphite were determined. It is experimentally established that the main parameters governing diamond crystallization processes are pressure, temperature, and run duration. The occurrence of Ca, Mg-phosphate, insoluble to phosphorus melt, is found to affect significantly the growth and morphology of diamond. The phosphate melt adsorbs selectively on the tetrahexahedral {310} faces giving rise to peculiar (321) growth steps. Crystallized diamonds were characterized by Fourier transform infrared (FTIR) absorption and Raman spectroscopy. It is found that with decreasing growth temperature both the strength of continuous absorption in the IR spectra and the width and asymmetry of the diamond Raman line significantly increases. The observed asymmetry of the diamond Raman line is suggested to be due to the Fano-type interference.