Theoretical study on the stability and mechanical property of Cr7C3

The ground state properties of Cr7C3 cell are studied in this paper by using first-principles calculations; the covalent bond in this compound is a kind of p and d hybridization between carbon (C) and chromium (Cr). The Fermi surface of projected density of states (PDOS) is dominated by d bands of Cr atoms and the whole structure has a metallic character. The calculated formation enthalpy is −116.55 and −120 kJ/mol for Pnma and Pmcn, respectively. We use two empirical equations of state (EOS) to investigate the lattice properties. The obtained average bulk modulus value is 308 GPa and the estimated mean shear modulus is 143.85 GPa, both of these two values are larger than Fe3C and Fe2B. The population analysis reveals some destabilization factors exist in Fe2B and Fe3C, but the attractive interactions for Cr7C3 are dispersed in the whole crystal. Due to the above reasons, we conclude that mechanical property and chemical stability of Cr7C3 are both much better than Fe2B and Fe3C.