Theoretical Study On Structures And Physical Properties Of Several Typical Binary Nitrides Under High Pressure

High pressure is an efficient means of obtaining new materials and discovering new laws.Crystal materials under high pressure have abundant phase transition sequences,greatly increasing the allotropy structure of materials.Therefore,high-pressure technology plays an irreplaceable and important role in the design and synthesis of new multifunctional materials.Many substances that cannot or are not easily synthesized under normal pressure can be prepared under high pressure,thereby obtaining new multifunctional materials.In this paper,the CALYPSO structure prediction methods combined with first principles calculation is used to study the crystal structure and physical properties of nitrogen oxides,platinum nitrogen compounds and zirconium nitrogen compounds under high pressure within the framework of density functional theory,and explore their potential applications,providing theoretical basis and guidance for the reverse design of new functional materials.The main research results are listed as follows:（1）The stable structures,electronic properties,and bonding characteristics of N₂O₅ compounds under high pressure were systematically studied using CALYPSO structural prediction methods combined with first-principles calculations.The results showed that two new structures have been discovered under high pressure,namely,P（?）and C2/c phases,with a phase transition sequence of P（?）→C2/c and a phase transition pressure of 28.1 GPa.The calculation results of phonon dispersion curves and elastic constants showed that both the P（?）and C2/c phases of N₂O₅ have dynamic and mechanical stabilities under high pressure.By analyzing the electron band structure and density of states results,it is found that N₂O₅ compounds are indirect band gap semiconductor materials,and their band gaps decrease with increasing pressure.The results of ELFs and Bader charges indicated that there are strong covalent bond interactions in N₂O₅ compounds,and their covalent properties increase with increasing pressure.（2）Through a combination of first-principles calculations and CALYPSO structural prediction methods,in-depth theoretical studies of platinum nitrogen compounds have been conducted,and the convex hulls of Pt-N systems in the range of0 to 100 GPa have been systematically established.The Pa3（?）-Pt N₂ synthesized in previous experiments was validated,and three stable platinum nitrogen compounds for P（?）-Pt N₄,P（?）-Pt N₅ and Pc-Pt₃N₄ with new chemical ratios were successfully predicted.And Pt N₂,Pt N₄,and Pt N₅ compounds can also exist stably under ambient pressure when released.By analyzing the crystal structures,electronic properties,superconducting properties,and energy density of materials,it is found that platinum nitrogen compounds are potential superconducting materials and high energy density materials.The superconducting transition temperature of the metallic Pc-Pt₃N₄ at 50GPa is 3.6 K.And semiconductor materials P（?）-Pt N₄ and P（?）-Pt N₅ will obtain about1.23 k J/g and 1.71 k J/g of energy when decomposed into Pt and N₂,respectively.（3）The structural evolution,mechanical properties and electronic properties of ZrN₂ compounds at 0～100 GPa were studied by using a combination of first-principles calculations and CALYPSO structural prediction methods.The results indicated that there are two new ZrN₂ compounds with C2/m and Pnma phases under high pressure,and the phase transition sequence at 17.6 GPa is C2/m→Pnma.The calculated elastic constants and phonon phonon dispersion curves showed that C2/m-ZrN₂and Pnma-ZrN₂ compounds are mechanically and dynamically stable.The calculation results of the electronic band structure show that C2/m-ZrN₂ has metallic properties and Pnma-ZrN₂ is a semiconductor with a band gap of 0.615 e V.In addition,it was confirmed by density of states and ELFs analysis that ZrN₂ compounds have the bonding property of covalent bond and ionic bond,which contributes a lot to its stability.Pnma-ZrN₂ is a potentially hard material with a Vickers hardness of 12.91 GPa at 0 GPa.In summary,the complex behavior of N₂O₅ compounds,Pt-N systems,and ZrN₂compounds under high pressure was investigated by studying their structures and properties.The structure and properties of N₂O₅ under high pressure have been explored,thereby enriching the theoretical study of nitrogen oxides under high pressure.It was found that Pt N₄ and Pt N₅ can be used as high energy density materials,and Pt₃N₄ is a potential superconductor,complementing the research on transition metal platinum group nitrides.ZrN₂ is a potential hard material.The research results of this paper provide a reference for the synthesis and design of new functional materials in the future.