Data in support of crystal structures of highly-ordered long-period stacking-ordered phases with 18R, 14H and 10H-type stacking sequences in the Mg–Zn–Y system

Abstract

The crystal structures of highly-ordered Mg–Zn–Y long-period stacking-ordered (LPSO) phases with the 18R, 14H and 10H-type stacking sequences have been investigated by atomic-resolution scanning transmission electron microscopy (STEM) and transmission electron microscopy (Kishida et al., 2015) [1]. This data article provides supporting materials for the crystal structure analysis based on the crystallographic theory of the order–disorder (OD) structure and the crystallographic information obtained through the structural optimization for various simple polytypes of the highly-ordered Mg–Zn–Y LPSO phases with the 18R, 14H and 10H-type stacking sequences by first-principles density functional theory (DFT) calculations.

Crystal structures of highly-ordered long-period stacking-ordered phases with 18R, 14H and 10H-type stacking sequences in the Mg–Zn–Y system

“…% Y, respectively. Such compositional deviations result in the multi-phase structures containing minor precipitates of the W-phase with an average chemical composition of Mg -47.0 ± 0.6 at.% Zn -26.6 ± 0.2 at.% Y in addition to major grains of LPSO phases for alloys A and B [24,35].…”

“…Since the lowest values are obtained for the structural models with the Mg addition, it is reasonable to consider that the Mg-Zn-Y LPSO/OD phases are stabilized most effectively by the Mg addition as concluded by Saal and Wolverton [27]. However, the differences in the formation energies and stability factors among four types of the structural models with or without an additional atom for each MDO polytype estimated based on the equations proposed by Saal and Wolverton [27] are less than about À30 meV/atom (see Table 1 in [35]). Considering that the k B T at room temperature is about 25 meV, the differences are relatively small and therefore, it is highly probable that the central site of each Zn 6 Y 8 atomic cluster is occupied by either Mg, Zn, Y or vacancy depending on the chemical composition of the LPSO phases related to the phase equilibrium.…”

“…STEM-EDS analysis confirmed that the average chemical composition of Mg -10.5 ± 0.4 at.% Zn -13.3 ± 0.4 at.% Y is quite close to the ideal values of Mg -10.0 at.% Zn -13.3 at.% Y (no additional atom in each Zn 6 Y 8 atomic cluster). The crystallographic parameters for the most stable polytype of the 10H-type Mg-Zn-Y LPSO/OD phase optimized using the VASP code are summarized in Table 5 [35]. The space group of Cmce differs from P6 3 /mcm that recently assigned for the 10H-type Mg-Zn-Y LPSO/OD phase formed in directionally solidified ingots of a Zn, Y-rich Mg-Zn-Y ternary alloy by Yamasaki et al [32].…”

“…The crystallographic parameters used to draw the projected crystal structures have been obtained by optimizing the crystal structure model without containing any additional atom at the central site by first-principles total-energy density functional theory (DFT) calculations using the Vienna ab initio simulation package (VASP) code (Table 3) [31]. The atomic coordinates for the central site in the Zn 6 Y 8 atomic cluster is also indicated in Table 3 for reference [35].…”

“…The ideal chemical composition of this 14H-type Mg-Zn-Y LPSO/OD phase is estimated to be Mg -7.1 at.% Zn -9.5 at.% Y (no additional atom in each Zn 6 Y 8 atomic cluster), which is in good agreement with Mg -6.7 ± 0.2 at.% Zn -9.8 ± 0.4 at.% Y obtained by STEM-EDS analysis. The crystallographic parameters for the 14H-type Mg-Zn-Y LPSO/OD phase obtained by the structural optimization by first-principles DFT calculations are summarized in Table 4 [35].…”