Substitution behavior of Cu doped into Fe3Si and its effect on the electronic structure and mechanical properties based on first-principles calculation

The substitution behavior of Cu doped into Fe3Si and its effect on the electronic structure and mechanical properties of Fe3Si were investigated using first principles plane-wave pseudopotential method based on density functional theory. Alloys with dopant Cu taking position of atoms Fe(I), Fe (II), and Si were labeled as Fe11CuSi4(I), Fe11CuSi4(II), and Fe12Si3Cu, respectively. The calculated formation enthalpy and cohesive energy of the three compounds and Fe3Si alloy were all negative, indicating their thermodynamic stability. However, the atomic fraction of dopant Cu substituting on Si atom was approximately zero, implying that the formation of Fe12Si3Cu is challenging. According to the analysis results of differential charge density and Bader charge, the covalent bond was weakened after Cu doping, while the ionic bond strength was in the order of Fe11CuSi4(I) > Fe3Si > Fe11CuSi4(II) > Fe12Si3Cu, which also indicated that the Fe12Si3Cu is less stable than the other three compounds. These results suggested that the dopant Cu atom preferred to substitute Fe atom, particularly Fe(I), but hardly substitute the Si atom. In order to gain a better understanding of the effect of Cu doping on the mechanical properties of Fe3Si compound, the antiphase boundary energy (ABPE) and elastic constants of Fe3Si, Fe11CuSi4(I), and Fe11CuSi4(II) were further calculated. The value of APBE was decreased, whereas the plasticity of Fe3Si compound is increased with the substitution of Fe atoms by the Cu dopant. The enhanced plasticity of Fe3Si alloy by Cu doping results from the dominant influence of the reduced APBE and weakened covalent bonds over the effect of reduction in ionic bonding. •Cu doped into Fe3Si compound prefers to substitute the Fe atom, particularly Fe(I), over Si atom.•The plasticity of Fe3Si compound is increased when Cu substitutes Fe atoms.•The enhanced plasticity by Cu doping is due to the dominant effect of the reduced APBE and weakened covalent bonds.