Ab initio study of the structural, elastic, and thermodynamic properties of tungsten monocarbide at high pressure and high temperature

Tungsten monocarbide (WC) exhibits unique physical and chemical properties. It is an indispensable industrial material used as cutting tools and has many potential applications in catalyst, energy storage, and so on. We performed calculations of the electronic structure in the framework of the density functional theory (DFT) with generalized gradient approximation (GGA) to investigate structural and elastic properties of WC. Bulk WC is very incompressible, but its bulk modulus is still smaller than diamond though Lin et al. reported that nano-crystalline WC was as incompressible as diamond. WC undergoes different compressibilities along a and c directions: the a-axis is more compressible than the c-axis. The ratio of shear modulus to bulk modulus (G/B) was studied and it was found that WC translated from the brittle to ductile state at ∼63 GPa. In order to compare with the EOS determined at finite temperature, the vibration effects of the crystal lattice are taken into account based on quasi-harmonic Debye model. The temperature effect on bulk modulus is discussed and the thermodynamic properties of WC, such as heat capacity CV, Debye temperature θD, and thermal expansion α, are calculated simultaneously.