First principles investigation of the substitutional doping of Mn in Mg2Ni phase and the electronic structure of Mg3MnNi2 phase

The substitutional doping of Mn in Mg₂Ni phase and the electronic structure of Mg₃MnNi₂ phase have been investigated by first principles density functional theory calculations. The calculation of enthalpy of formation shows that among the four different lattice sites of Mg(6f), Mg(6i), Ni(3b) and Ni(3d) in Mg₂Ni unit cell, the most preferable site of substitution of Mn in Mg₂Ni lattice has been confirmed to be Mg(6i) lattice site. The constructed Mg₉Mn_3Mg(6i)Ni₆ structure by replacing 3 Mg atoms at Mg(6i) lattice sites with 3 Mn atoms in the Mg₂Ni unit cell is less stable. In contrast, the cubic Mg₃MnNi₂ phase that has the same composition as that of Mg₉Mn_3Mg(6i)Ni₆ structure possesses good stability. Analysis of density of states (DOS) indicates that there is a strong hybridization between Mg s, Mg p and Ni d electrons, which is dominant in controlling the structural stability of pure and Mn-doped Mg₂Ni phases. The Mn-substitution in Mg₂Ni unit cell weakens the interaction between Mg s, Mg p and Ni d electrons, especially for Mg₉Mn_3Mg(6i)Ni₆ phase. The cubic Mg₃MnNi₂ phase possesses a strong hybridization between Mn and Mg, Ni atomic orbits under simultaneously retaining the strong bonding among Mg s, Mg p and Ni d electrons. Based on the calculated results, the stability of phases gradually decreases along the sequence pure Mg₂Ni phase > Mg₃MnNi₂ phase > Mn-substitution doped Mg₂Ni phase.