First-principles study of electronic and geometrical structures of semiconducting β-FeSi2 with doping

Electronic structure of β-FeSi2 and density of states (DOS) of subshells of Fe and Si were calculated, using the self-consistent full-potential linearized augmented plane wave method within the density functional theory. The general gradient approximation was used to treat the exchange and correlation potential. The DOS of β-FeSi2 is mainly composed of that of d-shell electrons of Fe and p-shell electrons of Si. For doped β-FeSi2, the internal parameters were relaxed, following the damped Newton dynamic schemes. The stable atomic substitution sites of doping atoms were determined by calculating the total energies for Fe0.9375Co0.0625Si2 and Fe(Si0.96875Al0.03125)2. The Fe atom at the FeII site and the Si atom at the SiI site are found to be preferentially substituted by Co and Al, respectively. This preferential substitution is in good agreement with the results of previous publications. Finally, the electronic structures of relaxed Fe0.9375Co0.0625Si2 and Fe(Si0.96875Al0.03125)2 were calculated and analyzed as well. The intrinsic relations between electronic structures of Fe0.9375Co0.0625Si2 and Fe(Si0.96875Al0.03125)2 and their respective thermoelectric properties including Seebeck coefficient, electrical conductivity and thermal conductivity are discussed in detail.