Ab Initio Study of Structural and Electronic Properties of Hexagonal BC2N

We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity.     

Chemical Synthesis of C3N and BC2N Compounds

A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.     

新型超硬C_5N晶体结构及性能的第一性原理研究（英文）

通过使用在晶体结构预测方面成熟的粒子群优化算法,提出了6种化学计量比为5∶1的氮化碳新相。采用基于密度泛函理论的第一性原理计算研究它们的结构、稳定性、机械性能和电子性质。计算结果表明,在提出的6种结构中,P62m-C_5N是能量最稳定的。弹性常数和声子谱计算表明,这些结构在0GPa时是机械稳定和动力学稳定的。电子计算显示,I4_1-C_5N是金属性的,而其他5种结构是半导体。维氏硬度计算表明,除I4_1-C_5N外,其余氮化碳都为超硬材料。通过形成焓计算,分析认为这6种结构能在目前实验所能达到的高压下合成(19~83GPa)。     

First-Principles Calculations of Phase Transition and Stability of Si2CN4 under High Pressure

A pressure-induced phase transition and stability in Si2 CN4 polymorphs under high pressure are studied by firstprinciples calculations. The result shows that the phase transition pressure of α- and β-Si2 CN4 to the cubic spinal phase is 29.9 GPa and 27.5 GPa predicted by thermodynamic method respectively. Under ambient condition, all of the three Si2CN4 polymorphs are metastable with positive formation enthalpy. Unlike the stability of Si3N4 polymorphs, α-Si2 CN4 is more stable than the β phase.     

Synthesis of Boron-Rich Cubic B（CxN1-x） Compounds

B2CN precursor is prepared by a mechanical vibration-milling process using amorphous boron, graphite and h-BN powders with mole ratio of 1：1：1. A mixture of precursor and Ca3B2N4 catalyst is treated under high pressure and high temperature. A boron rich cubic B（CxN1-x） phase is obtained after removing the catalyst by acid treatment. The average C content of the boron-rich cubic phase is about 6 at.% detected by energy-dispersive x-ray analysis spectroscopy. It is found that the highest carbon content in the cubic phase is as large as 16 at.%.