低压下一种新的聚合氮结构  

A novel low-pressure structure of polymeric nitrogen

作　　者：梁冬梅 刘海燕 甘云丹 匡安龙[1] 田春玲[1] Dongmei Liang;Haiyan Liu;Yundan Gan;Anlong Kuang;Chunling Tian(School of Physical Science and Technology,Southwest University,Chongqing 400715,China;Xi’an Institute of Modern Chemistry,Xi’an 710065,China)

机构地区：[1]西南大学物理科学与技术学院,重庆400715 [2]西安近代化学研究所,西安710065

出　　处：《科学通报》2021年第22期2908-2914,共7页Chinese Science Bulletin

基　　金：西南大学专业课程建设项目(5240101911)资助。

摘　　要：聚合氮作为潜在的清洁高能量密度材料有望取代传统的C、H、O、N含能材料,但是已发现的聚合氮结构无法保存到常规条件下.因此,获得能够存在于近常规条件下的聚合氮结构是人们比较关心的问题.本文结合第一性原理计算和CALYPSO晶体结构预测方法对低压下氮的结构进行搜索.在30 GPa下发现了一种由氮链和类连五唑构成的聚合氮结构,其空间群为Cm.通过焓差曲线分析发现,Cm聚合氮在10~35 GPa压强范围是目前发现的聚合氮结构中最稳定的相结构,其焓值较已知的偏转立方氮(cg-N)结构、N_(6)和N_(8)结构都低.声子色散计算和弹性常数计算表明,Cm聚合氮具有晶格动力学稳定性和力学稳定性;分子动力学模拟表明,Cm聚合氮在常温下卸压到一个大气压仍保持结构稳定.这预示着高压下合成的Cm聚合氮可能被截获和保留到常温常压条件下.Polymeric nitrogen is a material of high energy density with single bond(bond energy 160 k J/mol)or double bond(420 k J/mol)of nitrogen atoms under high temperature and high pressure.When polymeric nitrogen is completely decomposed into N2,the energy released by the change of bonding mode is higher than that of any other known non-nuclear explosion reactions,and the decomposed product is environmentally friendly nitrogen.Therefore,polymeric nitrogen is considered as one of the candidates for the new generation of energetic materials with high energy density.Many novel forms of polymeric nitrogen are predicted theoretically under high pressure,such as layered structure,chain structure,chair mesh structure,cage structure,and pure nitrogen metal salt P4/nbm structure.Experimentally,the polymeric nitrogen synthesized under extreme conditions includes cubic-biased nitrogen(cg-N),layered polymeric nitrogen(LP-N),hexagonal-layered polymeric nitrogen(P42 bc),and black-scale pleated polymeric nitrogen(BP-N),but these polymeric nitrogen structures cannot be preserved in ambient conditions.The latest theoretical calculation shows that the enthalpy of N_(8) and N_(6) polyatomic molecular crystals is lower than that of cg-N in the low-pressure region,which means that they are more stable than cg-N and can be stable at room temperature and ambient pressure,but they have not been synthesized in the experiment.In view of poor structural stability of polymerized nitrogen under high pressure,people need to obtain a new type of polymeric nitrogen that can be stable under nearly conventional conditions.Here,we have extensively explored the low-pressure crystal structures of nitrogen by first principles simulation combined with crystal structure prediction method.We found a polymeric nitrogen structure composed of a nitrogen chain and pentazole-like N11.The spatial symmetry group of the polymeric nitrogen is Cm.The structure proposed in this paper is different from traditional pentazole and has thermodynamic stability in a certain ra

关 键 词：CALYPSO 聚合氮 低压 第一性原理计算 分子动力学模拟 

分 类 号：TQ560.1[化学工程—炸药化工]