First-Principles Study On High Pressure Physical Properties And High Temperature Decomposition Behavior Of Barium Nitrides And Carbonitrides

With the continuous strengthening of national defense construction and economic development,the demand for high-energy materials with high energy density,high safety performance and environmental friendliness is increasing day by day.All-nitrogen compounds are a kind of energetic material with excellent properties,but the difficulty of synthesis and stability limit their application and development.It is found that the introduction of other metal or nonmetallic atoms can reduce the repulsive interaction of adjacent nitrogen pair electrons,resulting in relatively stable nitrogen-rich materials,such as barium nitrides and carbonitrides.As potential energetic materials,the behavior of these materials at high temperature and high pressure deserves attention.In this paper,the physical properties of barium nitrides and carbonitrides at high pressure and the decomposition behavior at high temperature were studied using the first-principles calculation method,and the following conclusions were obtained:（1）The effect of pressure on the structure,mechanical and electronic properties of Ba₂N,BaN₂,BaN₅ and BaN₆ were studied.The results show that four barium nitrides have good dynamic stability.The covalence of N-N bonds of BaN₂,BaN₅ and BaN₆increases with the increase of pressure,while the covalence of N-Babonds of Ba₂N decreases.The elastic constants and mechanical parameters of the four barium nitrides basically increase with the increase of pressure,indicating that the ability of these compounds to resist external forces is enhanced under pressure.（2）The effect of pressure on the structure,mechanical and electronic properties of C₃N₂,C₁₁N₄,C₃N₄,CN₂ and C₂N₂ were studied.With the increase of pressure,the bond length of C₃N₂,C₁₁N₄,C₃N₄ and CN₂ decreased,while the population increased,the bond lengths and populations of C-N and C-C bonds in C₂N₂ showed an opposite trend to those of the above four compounds with increasing pressure.The mechanical properties of the five carbonitrides increase with the increase of pressure.（3）Molecular dynamics simulation was used to analyze the structural and electronic properties of BaN₆ and C₂N₂ at high temperature.The results show that BaN₆ forms more N-Babonds at 2000 K and 2500 K,while the C-N bond is formed along with the C-C bond breaking of C₂N₂ at 2500 K.The band gaps of both BaN₆ and C₂N₂ decrease under the influence of temperature.