Crystal structure of the Al20Mn5.37Ni1.31 phase in the Al–Mn–Ni system

The phase Al20Mn5.37Ni1.31 in the ternary system Al–Mn–Ni system was synthesized by high-temperature sintering and its crystal structure has been refined from single-crystal X-ray data.

data reports (Taylor, 1959), or the decaaluminium trinickel iron phase Al 10 Ni 3 Fe 0.83 that was recently obtained in our group by highpressure sintering (HPS) of a stoichiometric mixture with nominal composition Al 71 Ni 24 Fe 5 (Wang et al., 2018). In the present study, the crystal-structure refinement of a phase with composition Al 20 Mn 5.37 Ni 1.31 based on single-crystal X-ray diffraction data is reported, in accordance with the SEM/EDX results (see Tables S2 and S3 along with Fig. S1 compiled in the supporting information). This phase is located within the diagram region of the ' phase determined previously (see Table S1 of the supporting information).
With respect to the Co 2 Al 5 structure type (Newkirk et al., 1961), in the crystal structure of the Al 20 Mn 5.37 Ni 1.31 phase the Co atoms are replaced by the transition metals Mn and Ni (Fig. 1). The asymmetric unit of Al 20 Mn 5.37 Ni 1.31 comprises five metal sites, three fully occupied by Al atoms at Wyckoff positions 2 a (Al1), 6 h (Al2) and 12 k (Al3), one partially occupied Ni2 site [occupancy 0.342 (2)] at 2 d and one cooccupied (Mn1/Ni1) site [occupancy ratio 0.895 (14): 0.105 (14)] at 6 h. The environment of the co-occupied (Mn1/ Ni1) site is shown in Fig. 2, where twelve vertices include ten Al atoms (Al1, Al2, Al3) and two symmetry-related (Mn1/ Ni1) sites. In the crystal structure, the distorted icosahedra centered at Al1 and (Mn1/Ni1) and the polyhedron centered at Al2 are fused with each other, as shown in Fig. 3.

Figure 3
The fusion of five polyhedra centered at one (Mn1/Ni1), two Al1 and two Al2 sites.

Figure 1
The crystal structure of Al 20 Mn 5.37 Ni 1.31 with two (Mn1/Ni1) sites and two Al1 atoms displayed with their coordination environments as polyhedra.
STA449C simultaneous thermal analysis apparatus. The sample was heated up to 1373 K for 10 min with a heating rate of 20 K min À1 . Finally, the sample was slowly cooled to room temperature by turning off the furnace power. Suitable pieces of single-crystal grains were selected from the products for single-crystal X-ray diffraction experiments.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. For better comparison with the Co 2 Al 5 structure type, the labelling scheme and atomic coordinates were adapted from Co 2 Al 5 (Newkirk et al., 1961). One of the five metal sites is partially occupied by Ni atoms (Ni2) and one site is co-occupied by Mn and Ni atoms (Mn1/Ni1); all Al atoms show full occupancy. Atoms sharing the same site were constrained to have the same coordinates and anisotropic displacement parameters. The maximum and minimum residual electron densities in the final difference map are located 1.32 Å from the (Mn1/Ni1) site and 0.01 Å from the same site, respectively.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.46 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.