First-Principle Calculations of the MgYA4 (A = Co and Ni) Phase with AuBe5-Type Structure

First-principles calculations have been performed to study the structural, mechanical and magnetic properties of the MgYCo4 and MgYNi4 phases in AuBe5-type structure. The obtained values of cohesive energy as well as formation energy prove that the MgYCo4 and MgYNi4 phases have a good combination of structural stability and alloying ability, which is also supported by electronic structure. It is found that the magnetic moment of the MgYCo4 phase is 19.06 µB per unit cell mainly owed to the 3d state of Co atom, and the MgYNi4 phase exhibits no magnetism. Both the trigonal shear constant C 44 and the shear modulus G of the MgYNi4 phase are larger than those of the MgYCo4 phase. Plasticity of alloys has been estimated by the C 11–C 12 and Young’s modulus E, and C 12–C 44, shear to bulk modulus ratio G/B and Poisson’s ratio ν have been studied to predict the ductility of alloys. According to the calculated results, the MgYCo4 phase has better plasticity as well as ductility, compared with the MgYNi4 phase.