新型超硬C5N晶体结构及性能的第一性原理研究

摘要

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-C5N是能量最稳定的.弹性常数和声子谱计算表明,这些结构在0 GPa时是机械稳定和动力学稳定的.电子计算显示,I41-C5N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I41-C5N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(19～83 GPa).%By using the developed particle swarm optimization algorithm on the crystal structural prediction,we proposed 6 novel carbon nitride phases with a 5∶1 stoichiometry.Their structures,stability,mechanical and electronic properties were investigated by first-principle calculations with the density functional theory.Our calculations indicate that P(6)2m-C5N is energetically favorable in the 6 structures.Both elastic constants and phonon-dispersion calculations show that these structures remain mechanically and dynamically stable at 0 GPa.Electronic calculations indicate that I41-C5N is metallic while the other 5 are semiconductive.The Vickers hardness shows that all the 6 structures are superhard materials except for I41-C5 N.Formation enthalpy calculations suggest that these 6 structures can be synthesized at attainable high pressures (19-83 GPa).