Ab initio study of phase stability and optical properties of TiN and VN nitrides in different phases

Abstract

Transition metal nitrides are ceramic materials known for their remarkable physical and mechanical characteristics, particularly their hardness. As part of this study, the structural, mechanical, electronic, phonon, and optical properties of nitrides were investigated. We focused on TiN in the NaCl–B1 and ZB-B3 phases and VN in the ZB-B3 using the density functional theory approach. The results show that the TiN equilibrium lattice constant in the NaCl–B1 phase is very close to what has already been reported. This confirms the overall reliability of the different phases. Furthermore, the heat of formation data suggests that TiN in both the NaCl–B1 and ZB-B3 phases is thermodynamically stable. The elastic constants confirm the mechanical stability of TiN in the NaCl–B1, ZB-B3, and VN in ZB phases. The bulk-to-shear ratio highlights that TiN in the NaCl–B1 phase exhibits brittleness, whereas TiN in the ZB-B3 phase displays ductility. Electronic band structure and total density of states calculations for both TiN in NaCl–B1 and ZB-B3 phases demonstrate their conductivity due to a pronounced valence-conduction overlap around the Fermi energy level. The low number of electrons accumulated at the Fermi energy level in the density of states (DOS) indicates electronic stability for TiN in the NaCl–B1 and ZB-B3 phases. The electron charge density plots indicate the presence of electrovalent (ionic) bonds between Ti-3d, V-3d, and N-2p. Additionally, the phonon dispersion curves reveal dynamical stability in both phases. Regarding optical properties in TiN, our predictions establish a distinct correlation between the loss function, reflectivity, and absorbance spectra within the 12.5 nm–25 nm energy range, with TiN in the NaCl phase exhibiting dominance. Notably, the NaCl phase exhibits higher absorption compared to the ZB phase, making it a promising candidate for use as a photocatalyst. Furthermore, the imaginary conductivity spectra align with the electronic properties, collectively indicating that these materials possess conductive characteristics.