The Analysis of the Transformation Mechanism of cBN Crystals with the First-Principle Calculation

Lichao Cai,Bin Xu,Meizhe Lv,Xiaohong Fan,Tifeng Jiao

doi:10.1155/2020/8653032

Lichao Cai, Bin Xu + Show 3 more

Open Access

https://doi.org/10.1155/2020/8653032

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Abstract

To clarify the synthesis mechanism of cubic boron nitride (cBN) with catalysts at high temperature and high pressure, we calculate the surface energy of the main phases in the Li-N-B synthesis system using the first-principle method. Based on the density functional theory, the surface energy of low-index surfaces of cBN, hexagonal boron nitride (hBN), and lithium boron nitride (Li3BN2) at the cBN synthetic temperature of 1700 K and synthetic pressure of 5.0 GPa is calculated. The surface energy of the main low-index surfaces of cBN is σ (111) > σ (001) > σ (110), that of hBN is σ 10 1 ¯ 0 > σ 11 2 ¯ 0 > σ (0001), and that of Li3BN2 is σ (100) > σ (110) > σ (001). The energy orders of the main low-index surfaces were well contrary to the corresponding orders of the valence electron density of the low-index surfaces of cBN, hBN, and Li3BN2, which were calculated by the empirical electron theory (EET) of solids and molecules. The result shows that the calculation results in this paper are well consistent with the previous results of the EET theory and support for the results of the “direct transformation of hBN to cBN under the catalysis of Li3BN2” obtained by the EET theory.

Highlights

Cubic boron nitride single crystals have a high hardness value, high melting point, high thermal conductivity, wide energy gap, and low dielectric constant, which make them highly attractive as promising materials [1,2,3,4]
The present Cubic boron nitride (cBN) single crystals still cannot meet the demand for advanced product development. e clear transformation mechanism of cBN crystals is significant to determine the quality of cBN crystals at HPHT. e research on the material surface and material catalysis mainly adopts the methods of characterization and theoretical research
The first-principle calculations based on the density functional theory became the most successful method and were applied widely in material calculations [12, 13]. e most stable surface of cBN crystals has been reported in detail using the CASTEP code [14, 15]

Summary

Introduction

Cubic boron nitride (cBN) single crystals have a high hardness value, high melting point, high thermal conductivity, wide energy gap, and low dielectric constant, which make them highly attractive as promising materials [1,2,3,4]. CBN single crystals are synthesized using hexagonal boron nitride (hBN) as raw materials and lithium nitride (Li3N) as catalysts by the static high-temperature and highpressure (HPHT) catalytic method [5,6,7]. In our previous experimental study, the main phases are hBN, cBN, and Li3BN2 in the interface layers [8]. The transformation possibilities from hBN to cBN and from Li3BN2 to cBN were discussed with the valence electron structure [9]. The analysis about properties of (110) surfaces of cBN crystals has been discussed systematically [16]. E characters and properties of (111) and (100) of cBN crystals have few reports in the previous studies [17, 18] The analysis about properties of (110) surfaces of cBN crystals has been discussed systematically [16]. e characters and properties of (111) and (100) of cBN crystals have few reports in the previous studies [17, 18]

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Conclusion