DISCRETE STEPS OF DIAMOND-GRAPHITE PHASE TRANSITION AT ANNEALING OF NANODIAMONDS IN WIDE TEMPERATURE RANGE

We present the short review of the works on a problem of phase transitions (PT) which are distributed in the temperature range Delta T of PT. Experimental studies of Raman spectra (laser wavelength 514.5 nm) of nanodiamonds after annealing at 900-2000 degrees C and their detailed numerical analysis with decomposition of the allocated oscillatory D and G bands on the compound spectral components D and G, D (k) and G (k') relating to various states of Brillouin's zones were conducted. Detection of temperature maxima of intensities, frequencies and full width at half maximum (FWHM) of individual Raman components as well as intensity of a background defines discrete steps of PT of diamond - onion-shaped carbon in temperature ranges of 940-1200 degrees C and 1500-2000 degrees C.