The temperature dependencies of the heat capacity at constant volume (C v ) and entropy (S) of qtz С 6 , qtz BN and qtz SiC are shown in Fig. in comparison with experimental C v data for diamond , cubic BN and cubic SiC . It is quite expected that the heat capacities of all three phases with quartz topology formed by distorted tetrahedra are higher than the heat capacities of the corresponding cubic phases.