First-principles study on the structural, elastic and electronic properties of Ti4N3 and Ti6N5 under high pressure

The structural, elastic and electronic properties of Ti 4 N 3 and Ti 6 N 5 have been systematically studied by first-principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) and local density approximation (LDA). Basic physical properties for Ti 4 N 3 and Ti 6 N 5 , such as the lattice constants, the bulk modulus, shear modulus, and elastic constants are calculated. The results show that Ti 4 N 3 and Ti 6 N 5 are mechanically stable under ambient pressure. The phonon dispersion spectra are researched throughout the Brillouin zone via the linear response approach as implemented in the CASTEP code, which indicate the optimized structures are stable dynamically. The Young’s modulus E and Poisson’s ratios [Formula: see text] are also determined within the framework of the Voigt–Reuss–Hill approximation. The analyses show that Ti 4 N 3 is more ductile than Ti 6 N 5 at the same pressure and ductility increases as the pressure increases. Moreover, the anisotropies of the Ti 4 N 3 and Ti 6 N 5 are discussed by the Young’s modulus at different directions, and the results indicate that the anisotropy of the two Ti–N compounds is obvious. The total density of states (TDOS) and partial density of states (PDOS) show that the TDOS of TiN, Ti 4 N 3 and Ti 6 N 5 originate mainly from Ti “d” and N “p” states. The results show that Ti 4 N 3 and Ti 6 N 5 present semimetal character. Pressure makes the level range of DOS significantly extended, for TiN, Ti 4 N 3 and Ti 6 N 5 . The TDOS decreases with the pressure rise, at Fermi level.