Ab initio study of structural, mechanical and electronic properties of 3d transitional metal carbide in cubic rocksalt (rs) , zincblende (zb) , and cesium chloride (cc)

Abstract

We have studied three structures of 3d transition metal carbides (TMCs) using LDA and GGA approximations. Interestingly, we found that the 3d TMCs (except ScC in rs, zb structures) have higher cohesive energy (Ecoh) than their nitrides indicating carbides are thermodynamically more stable. The computed values of Vickers hardness (Hv) of rs-TiC is about 25.66 GPa and are compatible with the experimental value, rs-TiC and rs-VC are the hardest carbides and even more complicated than their nitrides; this study can reduce the high cost and the time used in experimental discoveries which do not have promising properties. In addition, theoretical calculations can assist the discovery of new super-hard TMCs and grab experimental attention to possible material choices for obtaining desired physical properties; surprisingly, only two carbides in GGA approximation (CrC and MnC) and in addition to this CrC in LDA approximation in cesium chloride (cc) structure are mechanically stable.In contrast, all the 3d TMCs in rocksalt (rs) and seven in zincblende (zb) structures are mechanically stable. The general trend of charge transfer from 3d transitional metal to carbon indicates decreased ionicity and increased covalency along the series. The hybridization of p orbitals of carbon with d orbitals of metal plays a crucial role in determining the mechanical stability and hardness of 3d TMCs. The computation of the total density of states indicates that all the 3d TMCs except zb-TiC and zb-FeC in all phases are metallic. We observed that the elastic constant C44 is anti-correlated with the number of electronic states around EF.