Thermodynamic Analysis About Nucleation and Growth of Cubic Boron Nitride in the System BN-Li₃N Under High Pressure and High Temperature

In this paper, cubic boron nitride (cBN) single crystals were synthesized with lithium nitride as catalyst under high pressure and high temperature. A lot of nanometer-sized cubic boron nitride nucleuses were found in the near surface layer of cBN crystals by high resolution transmission electron microscopy examinations. Based on the experiment results, the transformation kinetics is described by a nucleation and growth process in the thermodynamic stability region of cBN. The theoretical description is based on the heterogeneous nucleation and layer growth mechanism, and the relevant parameters are estimated and discussed. The results show that critical crystal radius, r*, is increasing with the elevated temperature under the same pressure, and temperature is the main influence on it under lower pressure. At the same time, the results show that crystal growth velocity has different changing tendency with different pressure under proper synthesized scope. The effect of the catalyst is suggested to lower the activation enthalpy for nucleation. These results are well consistent with experimental data.