First-principles study on thermodynamic stability and electronic characteristics of long-period stacking ordered phases in Mg-Zn-Y alloys

摘要

A first-principles pseudopotential plane-wave method based on density functional theory has been used to investigate the thermodynamic stability and electronic characteristics of long-period stacking ordered (LPSO) phases in Mg-Zn-Y alloys. The obtained lattice constants of each LPSO phase considered are in good agreement with the experimentally determined values, with relative errors ranging from 0.21% to 2.0%. The calculated enthalpies of formation show that 14H and 18R phases can co-exist in the Mg-Zn-Y system, and the 18R phase is easier to form than the 14H phase while solidifying. But the 14H phase is more stable than the 18R phase by the calculation results of reaction energy. And the calculated results are in accord with the experiments for the thermodynamic stability of the two phases. The density of states of these phases reveals that the discrepancy in the stability of LPSO phases could be attributed to the variation of bonding electron numbers at low-energy region of Fermi level. In addition, the calculation of the charge density shows that the Zn-Y bond exhibits covalent feature in both 14H and 18R phases, and the covalent bonding of the 14H phase is stronger than that of the 18R phase, which means the 14H phase is more stable than the 18R phase. (C) 2017 Elsevier B.V. All rights reserved.