Abstract
The nucleation of cubic boron nitride (cBN) single crystals synthesized with lithium nitride (Li3N) as a catalyst under high pressure and high temperature (HPHT) was analyzed. Many nanometer-sized cubic boron nitride nuclei formed in the near surface layer, as detected by high resolution transmission electron microscopy. Based on the experiment results, the transformation kinetics is described by a nucleation and growth process in the thermodynamic stability region of cBN. A theoretical description is developed based on the heterogeneous nucleation and layer growth mechanism, and the relevant parameters are estimated and discussed. The critical crystal radius, r*, increases with the temperature under constant pressure; the change with temperature more pronounced at lower pressure (such as 4.5 GPa). The crystal growth velocity increased with the temperature, and it is parabolic with temperature under certain pressure. These results are consistent with experimental data.
Highlights
Cubic boron nitride single crystals, as a functional material, have many interesting properties, such as high thermal conductivity, high hardness second only to diamond and excellent chemical stability.they are typical III-V group semiconductor materials with a wide energy gap, which can be made into both p- and n-type with suitable impurity additions [1,2,3]
The powder in the near-surface region which surround the cubic boron nitride (cBN) crystal matrix were carefully collected under the view of an optic microscope, and their phases were determined by means of a JEM-2010F (JEOL Ltd, Akishima, Japan) type high resolution transmission electron microscope (HRTEM) with an operating voltage of 200 kV
The structures and morphologies of the near-surface region in cBN are closely associated with the crystal growth under high pressure and high temperature (HPHT), and it may be of great significance to explain the process of cBN growth [14,15]
Summary
Cubic boron nitride single crystals, as a functional material, have many interesting properties, such as high thermal conductivity, high hardness second only to diamond and excellent chemical stability. They are typical III-V group semiconductor materials with a wide energy gap, which can be made into both p- and n-type with suitable impurity additions [1,2,3]. Due to the differences in equipment and synthesis methods, researchers may draw the different conclusions from their experimental results Against this background, some work has been undertaken to investigate the kinetics of the phase transition and discuss the mechanism about nucleation and crystal growth. The mechanism of nucleation and crystal growth is still a subject for discussion, especially by thermodynamic analysis
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