Electronic structure, x-ray photoemission spectra, and transport properties ofFe3C (cementite)

Abstract

We have performed a detailed linear-muffin-tin-orbitals calculation of the electronic structure of ${\mathrm{Fe}}_3$C (cementite). The orthorhombic unit cell contains 16 atoms, with 4 Fe atoms taking type-1 positions which are not equivalent to the type-2 positions of the other 8 Fe atoms. The calculated moments in the ferromagnetic state are μ=1.98${\mathrm{\mu }}_{\mathit{B}}$ on the Fe(1) sites, μ=1.74${\mathrm{\mu }}_{\mathit{B}}$ on the Fe(2) sites, and μ=-0.06${\mathrm{\mu }}_{\mathit{B}}$ on the carbon sites, in excellent agreement with experiment. The hyperfine fields in ${\mathrm{Fe}}_3$C have been calculated from the spin densities at the center of each atom. We obtain B=26.9 T on the Fe(1) sites, B=25.7 T on the Fe(2) sites, and B=0.23 T on the carbon sites. The calculated electron states are in qualitative agreement with x-ray photoemission spectroscopic data. The electron-phonon coupling parameter estimated from our calculations is λ=0.77. This gives an electronic heat capacity close to the experimental one. Experimental data on the electrical resistivity are uncertain and larger than our estimated value ρ=47 μΩ cm at 300 K. The calculated cohesive energy per atom ${\mathit{E}}_{\mathrm{coh}}$=615 mRy is to be compared with the estimate ${\mathit{E}}_{\mathrm{coh}}$=370 mRy based on experimental information.