Electronic Structure and Structural Properties of Ti₄AlN ₃ Investigated by Ab initio Calculations

The crystal structure, electronic structure and chemical bonding of Ti ₄AlN₃ have been investigated by ab initio pseudopotential calculations. The equilibrium lattice parameters, atomic positions in the unit cell and bond lengths have been obtained by minimizing the total energy. The differences between the calculated and measured lattice constants are generally less than 1%. The electronic structure of Ti₄AlN₃ shows a metallic-like character and the 3d states of Ti dominate its electronic conductivity. The chemical bonding in Ti₄AlN₃ is an anisotropic metallic-covalent-ionic character. Ti_I,II and N atoms form strong covalent ionic bond in the Ti_II-N_II-Ti _I-N_I-Ti_I-N_II-Ti_II-Al unit chain, while the bonding between Ti_II and Al is relatively weak. The strong covalent and ionic bonding in Ti₄AlN₃ is responsible for its high modulus and strength, while the metallic bonding results in its metallic properties. This kind of anisotropic bonding character results in the anisotropic properties of Ti₄AlN₃.