Synthesis of new cubic C3N4 and diamond-like BC3 phases under high pressure and high temperature

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In this report, we discuss the progress in synthesis of new binary phases from B-C-N triangle in DAC under high-pressure and high-temperature (HPHT) conditions: cubic C3N4 (c-C3N4) and diamond-like BC3 (d-BC3) phase. These two phases have been synthesized by direct transformation from graphitic phases under HPHT conditions. The c-C3N4 phase was recovered at ambient conditions from the graphite-like C3N4 (g-C3N4) phase subjected to pressures between 21 and 38 GPa in a diamond anvil cell, laser-heated to temperatures between 1600 and 3000 K. The x-ray diffraction data on the new phase are best explained by a cubic unit cell with the lattice parameters a = 3.878±0.001 Å. The synthesis of the c-C3N4 phase has been also conducted in a large volume press at pressure 25 GPa and temperature 2000°C. X-ray peaks of c-C3N4 phase obtained in the large-volume press are weaker than those of diamonds. Application of the UV Raman spectroscopy revealed that UV Raman spectrum of the g-C3N4 is substantially different from that measured with visible Raman spectroscopy. It has two strong peaks at 690 cm-1 and at 986 cm-1 assigned to different types of the ring (s-triazine ring) breathing modes. A diamond-like BC3 has been synthesized at temperature 2033 ± 241 K and at pressure 50 GPa. The conclusion about the phase transition from graphitic BC3 (g-BC3) to d-BC3 phase was made from the analysis of Raman scattering data. The Raman spectrum of the novel d-BC3 displays all the peaks but one at 671 cm-1 characteristic to Raman spectra the B doped diamond. The peaks pattern of the d-BC3 suggests that this phase could become a superconductor at low temperatures.