Electronic structures mechanical and thermal properties of V-C binary compounds

The electronic structure, mechanical and thermal properties of VC, alpha-V2C, beta-V2C, V4C3, V6C5 and V8C7 are investigated systematically by the first principles calculation using density functional theory combined with the Debye quasi-harmonic approximation. Formation enthalpy is calculated and used to estimate the stability of the V-C binary compounds. The electronic structures and chemical bonding characteristics are analyzed by the band structures, density of states and Mulliken population analysis. The elastic constants of single crystal, hardness, bulk, shear, Young's modulus and Poisson's ratio of the polycrystalline crystal are obtained and compared with the experimental results. The anisotropic mechanical properties are discussed using the anisotropic index, three-dimensional surface contours and their planar projections on different planes of the bulk and Young's modulus. VC exhibits the largest mechanical modulus because of its strong chemical bonding and alpha-V2C reveals the weakest elastic anisotropy. The specific heats at constant pressure and volume and the thermal expansion coefficients of the V-C binary compounds versus T from 0-1000 K are calculated and the largest and smallest thermal expansion coefficients are attributed to alpha-V2C and V4C3, respectively.