During a resent years a grate attention was given to the problem of an investigation of phase transitions in C₃N₄ as by M.L.Cohen and co-authors were theoretical predicted the diamond-like properties of beta-C₃N₄. We investigated the phase transitions in the two samples of this material, which were prepared by different methods (chemical (1) and shock (2)), in the carbonado-diamond anvil cell with using the methods of electrical measurement on d.c. and impedance spectroscopy. The first sample were investigated at pressure 15GPa-43GPa, a second sample at pressure less 33GPa. A dependences of the electrical resistances R of the samples at the T=300K, in the 10³Hz<f<8*10⁵ Hz were made. A hodographs of impedance and a tangency of an angle of dielectric loss dependencies were got.
For the sample No.1. impedance measurement give a little hysteresis and a weak indication on the existence of phase transitions at 15GPa-25GPa and 33GPa-35GPa. After unloading the sample on 2-4-cycles input-output, the R is sharply increased more than 10⁴ times and large hysteresis is appeared (d.c.). After holding under pressure 43GPa during 6 days hysteresis has vanished. After fast increasing of pressure till 43GPa (2 minutes) some reaction has taken place and after unloading was got a graphite dust and transparent small crystallite of unknown nature. The preliminary results obtained shows the new phase appearing from C3N4 under pressure till 43GPa at room temperature and phase transitions under 15-25GPa and 33-35GPa possible with changing composition. For the sample No.2. the results are differ from results for sample No.1. The resistance is decreasing with increase the pressure.
So the method of preparing samples and their purity is essential for behavior their electrical conductivity.
This work in part has been supported by RFBR (grant No.01-03-96494,02-03-32699), CRDF (grant No.REC-005).

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