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 Mg9Mn3Mg(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 Mg9Mn3Mg(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 Mg9Mn3Mg(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. (C) 2010 Elsevier B. V. All rights reserved.