Аннотация:A new method was developed for the preparation of bulk samples of carbon nitride on exposure of an amorphous nitrogen- and carbon-containing material to high temperature and ultrahigh pressure in the presence of crystallization seeds. Amorphous carbon nitride whose composition was close to C 3N4 was used as a starting material. Thin films of crystalline carbon nitrides prepared by the laser-electric discharge method were used as crystallization seeds. The samples were evaluated by X-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy, Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Notably, XPS studies of the samples demonstrate that the nitrogen composition in α-C3N4.2 material initially containing more than 58% nitrogen decreases during the thermobaric process and reaches a common, stable composition of 45%. The thermobaric experiments were performed at 10-77 kbar and 350-1200 C.