Structural, elastic and thermodynamic properties of iron carbide Fe7C3 phases: An ab initio study

Using ab initio spin-polarized density functional theory calculations, the structural, elastic and thermodynamic properties of the orthorhombic and hexagonal phases of the iron carbide Fe7C3 were investigated. The calculated ground-state lattice parameters are in good agreement with the available corresponding theoretical and experimental data. The single-crystal and polycrystalline aggregate elastic constants, sound velocities, Debye temperature, brittle/ductile character and elastic anisotropy have been estimated. The calculated bulk modulus values of both considered phases are very close and are approximately equal to 262 GPa, which classifies the title compounds among the hard materials. The temperature and pressure dependencies of the unit-cell volume, bulk modulus, volume thermal expansion coefficient, isochoric and isobaric heat capacity, and Debye temperature were investigated using the quasi-harmonic Debye model.