First-principles Study Of Two Ternary Nitrides TMWN₂ And A-M-N Structures

Metal nitrides have excellent physical and chemical properties such as high temperature resistance,corrosion resistance,friction resistance,oxidation resistance and good electrical and thermal conductivity.It has attracted extensive attention in the fields of optics,electronics and magnetism.In this paper,the crystal structure,elastic properties and electronic structure of TMWN₂ and A-M-N ternary metal nitrides are studied.The electronic structure,elastic properties and magnetic properties of TMWN₂(TM=Cr,Mn,Fe,Co)have been studied by first principles calculations.First of all,the basic structural units of Cr/Fe/Co WN₂ are TMN₆ octahedron and WN₆ tri-prism,and the basic structural units of Mn WN₂ are Mn N₄ tetrahedron and WN₆ octahedron.TMN₆ octahedron/Mn N₄ tetrahedron and WN₆ tri-prism/octahedron are stacked along the c-axis to form TMWN₂.Secondly,the calculation results of electron localization function,crystal orbital Hamiltonian population and Bader charge show that both TM-N and W-N bonds are formed by the interaction of covalent and ionic bonds.Then,through the analysis of Young's modulus of TMWN₂,it is found that TMWN₂ are anisotropic,and Co WN₂ has the strongest anisotropy.Finally,when the GGA method is used for calculation,the results of the band structure show that TMWN₂ are metallic.When GGA+U method was used,Cr/Fe/Co WN₂show semiconductor characteristics with the increase of U value,while Mn WN₂ still maintains metallic properties.Based on density functional theory,the analysis of A-M-N(A=Zn,Mg;M=Sb,Mo,W,Nb,Ti,Zr,Hf)was calculated by first principles,and systematically studied the crystal structure,electronic properties and elastic properties of this system.Among them,Zn-M-N(M=Sb,Mo,W)is wurtzite structure,and Mg-M-N(M=Nb,Ti,Zr,Hf)is rocksalt structure.In the Zn-M-N structure,the basic structural units are Zn N₄ tetrahedron and MN₄ tetrahedron,and in the Mg-M-N structure,the basic structural units are Mg N₆octahedron and MN₆ octahedron.The calculation of band structure shows that A-M-N are all semiconductors.Zn₂Sb N₃,Mg Zr N₂ and Mg Hf N₂ are direct bandgap semiconductors,and Zn₃Mo N₄,Zn₃WN₄,Mg₂Nb N₃ and Mg Ti N₂ are indirect bandgap semiconductors.Zn₃Mo N₄ and Zn₃WN₄ have relatively large band gaps of 2.95 e V and 3.65 e V,respectively.The band gaps of the other structures are almost between 0.9 and 1.7 e V.The analysis of Young's modulus shows that A-M-N have anisotropy,and Mg₂Nb N₃ has the strongest anisotrop.The calculation of electron local function,crystal orbital Hamiltonian population and Bader charge shows that the covalent interaction of M-N bond is very strong,which plays a very important role in the stability of the structure.