The thermodynamic properties of the new phases were calculated from the phonon frequencies using the statistical thermodynamic approach on a high-precision sampling mesh in the Brillouin zone. The temperature dependencies of the heat capacity at constant volume (C V ) and entropy (S) of cfc С 8 , 4H BN and hexagonal BC 2 N are shown in Fig. in comparison with experimental data for diamond and wurtzite BN . It is quite expected that the thermodynamic properties of cfc C 8 and 4H BN are close to those of diamond and wurtzite BN, respectively. As for hexagonal BC 2 N, its heat capacity and enthalpy, which are intermediate between C 8 and 4H BN, are in surprising agreement with the experimental data for wBN, but significantly different from the data for diamond.