Theoretical Study On High-pressure Physical Properties Of Typical Azotetrazole Nonmetallic Energetic Salts

Energetic materials can release huge energy under certain external stimulation,which have become the main sources of power in civil industry and military.Among them,azotetrazole nonmetallic energetic salts have attracted great attention because of their advantages of large gas production,high safety,high product pollution-free and so on.At present,the research on such materials mainly focused on the state of normal temperature and pressure.In fact,the decomposition and initiation of energetic materials often involve extreme conditions of high temperature and high pressure,and the pressure will change the internal microscopic properties,thus affecting the macro behavior such as detonation and safety.Therefore,the study on the high-pressure physical properties of azotetrazole nonmetallic energetic salts is helpful to understand the influence of pressure on their microstructure and properties,and provide theoretical guidance for safe transportation and effective use.In this paper,the crystal structures,electronic structures and mechanical properties of three typical azobazolium nonmetallic energetic salts GZT,TAGZT and AFZT under the pressure of 0～50 GPa are studied by using first-principles calculation method based on density functional theory,and the relation between these properties and their sensitivity are discussed.Firstly,the basic physical properties of GZT,TAGZT and AFZT at zero pressure were studied.They belong to monoclinic system.The ions in GZT and TAGZT are mainly distributed along the yz plane,while the ions in AFZT are mainly distributed along the xz plane.The three energetic salts have indirect band gaps of similar size.The hydrogen bond interactions of N-H…N type play the dominant role in their structures,and abundant hydrogen bonds are distributed in GZT and TAGZT structures,while hydrogen bonds in AFZT are sparse,which is one of the reasons why it shows the highest sensitivity.Their mechanical properties are stable at zero pressure.GZT and TAGZT mainly show toughness,while AFZT shows brittleness.Secondly,the structural stability and mechanical properties of the three energetic salts under high pressure are studied.The results show that AFZT and TAGZT crystals undergo structural transformation at 5 GPa and 29.4 GPa,respectively,while GZT has no structural transformation.In addition,all of them show anisotropy in mechanical properties,and they show stronger deformation resistance in the direction of crystal axis with dense distribution of hydrogen bond interactions.The pressure enhances the rigidity of the three energetic salts,which also leads to the transformation of AFZT from brittle to ductile at 10 GPa.Finally,the effects of pressure on the electronic structures of three energetic salts are studied.The band gap of TAGZT is zero at 29.4 GPa,while that of AFZT is mutated at 5GPa,suggesting that the structural transformation will be accompanied by the internal electronic structure transformation.Under pressure,the total density of states of them move towards to lower energy level,and the degree of electron localization decreases.The range of interatomic interactions is expanded and the distances are shortened,and the short-range intermolecular forces are increased.For these three azotetrazole nonmetallic energetic salts,the results show that the intensity of the response to pressure is related to their sensitivity: the AFZT with the highest sensitivity has the lowest pressure point of structural transformation and the lowest pressure point of mechanical instability.The GZT with the lowest sensitivity has no structural transformation under 0～50 GPa and has the highest pressure point of mechanical instability.