Effects of Pressure on Structural, Mechanical, and Electronic Properties and Stability of Fe_xSi_y Compounds

Herein, the pressure dependence of the structural, mechanical, and electronic properties is investigated for Fe₂Si, FeSi, Fe₃Si, α-FeSi₂, β-FeSi₂, Fe₅Si₃, and Fe₁₁Si₅ in the pressure range of 0–100 GPa based on density functional theory. The calculated lattice constants are in good agreement with the experimental results. The order of the thermodynamic stability of the seven structures is FeSi > Fe₅Si₃ > Fe₂Si > β-FeSi₂ > Fe₁₁Si₅ > α-FeSi₂ > Fe₃Si. The electronic properties are analyzed including density of states and band structures. The mechanical properties of FeSi, Fe₂Si, Fe₅Si₃, α-FeSi₂, and β-FeSi₂ are studied thoroughly: The elastic constants are obtained under different pressures; the mechanical stability under the considered pressures is evaluated by the stability criteria. The results show that FeSi, Fe₅Si₃, and β-FeSi₂ are mechanically stable at pressures from 0 to 100 GPa; Fe₂Si is unstable under compression; and α-FeSi₂ is unstable in the range of 60–100 GPa. The values of B, G, and E are calculated, which indicate that the ability to resist deformation of the material increases with the increase in pressure. The B/G values are calculated, suggesting that both Fe₅Si₃ and Fe₂Si are ductile materials; the brittle–tough transition is observed in FeSi, α-FeSi₂, and β-FeSi₂.