High Pressure Design And Research Of High Energy Density Materials ZnN₆ And CO

In recent years,China's national defense industry has continued to develop,and the environmental pollution caused by energetic materials has become increasingly serious.Traditional energetic materials will produce numerous of toxic,complex and difficult-to-decompose pollutants throughout their life cycle.If these pollutants cannot be disposed of quickly or correctly,they will pollute the environment and even harm human health.It is of great significance for the development of national defense industry to find High Energy Density Materials(HEDMs)which can improve the properties of energetic materials.In addition,high energy density materials can reduce the generation of pollutants in both production and use,which plays an important role in reducing environmental pollution.Nitrogen-rich energetic materials and carbon-oxygen energetic materials have higher enthalpy of formation,and their performances are better than that of traditional energetic materials,mainly because there are a lot of nitrogen-nitrogen bonds and carbon-oxygen bonds in the molecules.The chemical bond energies of nitrogen-nitrogen bond and carbon-oxygen bond are 794 k J/mol and 745 k J/mol respectively,which are higher than other common chemical bond energies.Although pure polymerized nitrogen energetic materials have high energy density,their application and development are limited by the characteristics of instability in normal pressure and room temperature and strict synthesis conditions.In view of this,metal nitrides as energetic materials have been paid more and more attention.In order to explore the potential of metal nitrogen compounds and carbon oxide compounds as high energy density materials,this article takes ZnN₆ and CO as examples.The extra nuclear electron distribution of Zn is 3d¹⁰4s²,which exhibits special electronic properties under high pressure;CO and N₂ are isoelectronics,and CO and N₂have similar crystal structures,phase diagrams,and non-molecular phase transitions.CO and N₂ have a strong similarity under low pressure,but there is a significant difference in high pressure.This paper mainly based on density functional theory and through the CALYPSO structure search software to design the structure of ZnN₆ and CO crystal,and through VASP software to the crystal design of detailed calculation and research,explore its potential as high energy density materials,the calculation results are as follows:(1)Research on the properties of high energy density material ZnN₆ crystal.Based on the first principles and density functional theory,the possible stable crystal structure of ZnN₆ in the pressure range of 0-200 GPa was studied by CALYPSO program.An I4₁md-ZnN₆ crystal that can exist stably on normal pressure and room temperature is designed,in which nitrogen atoms are polymerized into a network structure with an energy density of4.7 k J/g,which has the potential as a high energy density material.At the same time,the structure has good dynamic stability and thermodynamic stability,with a band gap of 3.26e V,and has semiconductor properties.And put forward a theoretical path to synthesize I4₁md-ZnN₆ crystal,which provides theoretical guidance for experimental synthesis.(2)Research on the properties of high energy density material solid CO crystal.Based on first principles and density functional theory,and through the CALYPSO program,the possible stable crystal structure of carbon monoxide in the pressure range of 100-5000 GPa was studied.Three types of CO that could exist stably under normal pressure and room temperature were designed,the spatial symmetry groups are I4m2,Pna2₁,C2/c,respectively.The I4m2-CO crystal is divided into upper and lower layers,and carbon atoms and monoxide atoms are connected to each other to form a ring structure and a network structure,respectively.In the Pna2₁-CO crystal,the carbon atoms and oxygen atoms are connected to each other to form a zigzag chain.While in the C2/c crystal,carbon atoms and oxygen atoms are connected to each other to form a six-membered ring.The three crystals have good thermodynamic and dynamic stability under normal pressure and room temperature.The calculated energy densities are 10.49,13.29,and 16.59 k J/g,respectively,and the mass density is 3.78?4.2?5.2 g/cm³,indicating that the three designed crystals both have the potential as high energy density materials.The electronic properties of I4m2-CO,Pna2₁-CO and C2/c-CO are calculated,and the band gaps are 2.4,2.2 and 3.5 e V,respectively,indicating that all the three crystals are semiconductor.