Formation of Diamond Embryos in the Region of Thermodynamic Stability as a Result of Direct Phase Transition Graphite-Diamond of Martensitic Type

In a stochastic approximation, taking into account the conclusions of the theory of elasticity for micro nonhomogeneous media, a model of diamond nucleation in a high-pressure chamber (HPC) is considered as a result of the direct graphite–diamond phase transition. Considerations are presented regarding the distribution of the number of nuclei N as a function of the intensive parameters pressure P and temperature T. The assumption that the number of grown diamond crystals equals the number of formed diamond nuclei made it possible to use the normal distribution (Gaussian distribution) for analyzing the diamond nucleation processes. As a result, a probabilistic analytical expression for the number of nuclei was obtained, allowing for sufficiently accurate determination of N depending on the measured pressure (P_meas) and temperature (T_meas) values. The rate of diamond nucleation was estimated within the framework of a martensitic-type phase transition model.