Structure Design And Physical Properties Of Aluminum Nitrides Under High Pressure

Polymeric nitrogen has a wide application prospect in many fields.The search for new high energy density materials(HEDMS)has become a key topic of scientific research.Due to the large energy difference between N-N or N=N and N?N,when N-N or N=N is transformed into N?N,huge energy will be released.Therefore,polymeric nitrogen is a potential material with high energy density.The decomposition product of polynitrogen in use is nitrogen,which has no pollution to the environment,so polynitrogen is an environment-friendly high energy density material.Finding polymeric nitrogen with low stable pressure is a hot issue in the field of high energy density materials.In this work,aluminum nitrides were selected as the research object.Using CALYPSO crystal structure prediction method and element substitution method,combined with the first principle calculation method,the crystal structure,thermodynamic and dynamic stability,electronic structure and other properties of aluminum nitrides under high pressure were systematically studied in the pressure range of 0-50 GPa.The following research results were obtained:1.Three new structures were found by crystal structure prediction method,namely P-1-Al₂N_3,P-1-Al₃N₅and P-1-Al N₄.Except P-1-Al₂N₃,the latter two structures are polymerized nitrogen structures containing N-N,and the density of states are 2.16 k J/g and 3.57 k J/g respectively,which are potential high energy density materials.2.The kinetic stability analysis of the above compounds shows that the kinetic properties of P-1-Al₂N₃are unstable,but P-1-Al₃N₅and P-1-Al N₄are dynamically stable at atmospheric pressure and high pressure.P-1-Al₃N₅is a semiconductor and P-1-Al N₄is a conductor.The largest contribution is the 2p orbital of nitrogen atom.The stable pressures of P-1-Al₃N₅and P-1-Al N₄are 5.8 and 21 GPa respectively,which is much lower than the cg-n synthesized in the experiment,which meets the requirements of new high energy density materials.3.C222₁-Al₃N₅compound obtained by element substitution method is dynamically stable at ambient pressure and 10 GPa,indicating that it may be synthesized under high pressure.The C222₁-Al₃N₅is a semiconductor.The structure is a polymeric nitrogen structure containing N-N,and the density of states is 3.87 k J/g,which is a potential high energy density material.