Theoretical study on structural, mechanical and electronic properties of ternary mononitride Ti0.5W0.5N from first-principles calculations

Abstract

In the present work, systematic structure searching is carried out using CALYPSO (Crystal structure AnaLYsis by Particle Swarm Optimization) method combined with first-principles calculations, in the pressure range of 0–300 GPa for ternary mononitride Ti0.5W0.5N. A new possible structure with Cmc21 space group has been uncovered to be the ground-state phase which is much more energetically favorable than the well known B1 structure at 0 GPa and 0 K conditions. There is an excellent enhancement of mechanical properties for the Cmc21-Ti0.5W0.5N relative to B1–Ti0.5W0.5N and its parent compounds B1–TiN and NbO-type WN. The dynamical, mechanical and thermodynamic stabilities are verified through calculating the phonon spectra, elastic constants and formation enthalpy. The elastic properties are fully investigated and the results show that its Vickers hardness value is up to 34 GPa evaluated from bulk modulus (335 GPa) and shear modulus (255 GPa), wihch is much more than that of B1–TiN and NbO-type WN. Meanwhile, the elastic anisotropy is also studied through the dependence of Young's, linear bulk and shear moduli along the crystal orientations. According with the elastic properties, the calculated ideal strengths also confirm that there is a great improvement for the Cmc21-Ti0.5W0.5N relative to that of the above binary mononitrides. Further analysis of the electronic density of states and the chemical bonding nature reveals that the component of Ti plays an important role through tuning the valence-electron concentration (VEC) to enhance the stability and the mechanical properties.