THE PRESSURE AND TEMPERATURE PARAMETERS O F STATE OF GRAPHITE AND DIAMOND SINGLE-CRYSTALS IN THE VICINITY OF P-T LINE OF THE DIRECT GRAPHITE - DIAMOND TRANSFORMATION

Tensor equations of state for hexagonal and cubic single crystals are derived. The pressure and temperature parameters of the above equation s are established for graphite and diamond. They relate unit strain on the crystals to zero and first P - T derivatives of their compressibi lity and thermal dilatation. Diagonal elements DELTA(ii) of the matrix of carbon atomic concentration jumps at the graphite-diamond interfac e are determined in the P - T region which embraces formation of prima ry covalent bonds in graphite and the graphite-to-diamond transformati on. A position of the P - T line of the direct graphite-to-diamond tra nsformation is refined from the magnitude of DELTA33.