Structural, elastic and electronic properties of β′ phase precipitate in Mg–Gd alloy system investigated via first-principles calculation

The β′ phase precipitate in Mg–Gd alloy system has been investigated by means of first-principles calculation within the generalized gradient approximation. The lattice parameters are determined theoretically by structural optimization of full relaxation, and the Mg7Gd is found to be energetically more stable compared with the Mg15Gd from the calculated formation energy. The nine independent elastic constants are calculated, indicating the proposed Mg15Gd structure in literature is mechanically unstable. Then the polycrystalline bulk modulus B, Young's modulus E, shear modulus G, Poisson ratio ν of Mg7Gd are gained by the Voigt–Reuss–Hill (VRH) approximation. The ductility and plasticity, especially elastic anisotropy are discussed in details. Based on the electronic density of states and charge density distribution, the covalent bonding and metallic bonding are exhibited in Mg7Gd compound. Last, the Debye temperature is also calculated for the investigation in the future.

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