Effect of Fe doping on structural, elastic and electronic properties of B2–ZrCu phase under hydrostatic pressure: A first-principles study

Highlights: • High pressure not only stabilizes the structure, but also enhances the ductility of non-doped Zr₈Cu₈ and doped Zr₈Cu_8-xFe_x (x=1, 2, 3). • The electron density topology is closely related to the ductility/brittleness of all compositions. • The equation of state for B2–ZrCu is established. The results are in good agreement with previous experimental measurements. The effects of Fe doping and applied hydrostatic pressure on structural, mechanical and electronic properties of Zr₈Cu_8-xFe_x (x = 0, 1, 2, 3) are investigated via the first-principles calculations. The equation of state (EOS) is established for B2–CuZr crystalline structure. The values are in good agreement with previous experimental results. The phase stability is improved simultaneously by the substitution of Fe for Cu and enhanced hydrostatic pressure for Zr₈Cu_8-xFe_x (x = 0, 1, 2, 3). Doping concentration plays an important role in tuning the values of bulk modulus B. However, the values of Vickers hardness $H_V$ follows the sequence as: Zr₈Cu₆Fe₂ > Zr₈Cu₇Fe₁ > Zr₈Cu₅Fe₃ > Zr₈Cu₈ (0–30 GPa). The sequence of B/G, Poisson's ratio is just opposite to that of $H_V$. It implies a strong correlation between ductility and charge density topology (closely related to bonding character and substitutional atomic sites). Substitution of Fe for Cu tailor the metallic characteristic of Zr–Cu bond into more directional covalent characteristic of Zr–Fe bond, thus make doped Zr₈Cu_8-xFe_x (x = 1, 2, 3) harder and more brittle than non-doped Zr₈Cu₈. The hydrostatic pressure generally enhances the predominant metallic character of Zr₈Cu_8-xFe_x (x = 0, 1, 2, 3), thus make all doped and non-doped compositions transit into a more ductile regime. The combined effects of directional bonding and pressurizing thus make Zr₈Cu₆Fe₂ (0 GPa) the most hard and brittle material and Zr₈Cu₈ (30 GPa) the most ductile material among all compositions.