Crystal structure of AlFe0.95

Liu, Y.; Liu, H.; Fan, C.; Bin, W.; Zhang, L.

doi:10.1107/S2414314623010659

inorganic compounds

IUCrDATA

ISSN: 2414-3146

Volume 8| Part 12| December 2023| x231065

https://doi.org/10.1107/S2414314623010659

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Crystal structure of AlFe_0.95

Yibo Liu,^a Huizi Liu,^a Changzeng Fan,^a,^b ^* Wen Bin ^a and Lifeng Zhang ^c

^aState Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, People's Republic of China, ^bHebei Key Lab for Optimizing Metal Product Technology and Performance, Yanshan University, Qinhuangdao 066004, People's Republic of China, and ^cSchool of Mechanical and Materials Engineering, North China University of Technology, Beijing, People's Republic of China
^*Correspondence e-mail: chzfan@ysu.edu.cn

Edited by S. Bernès, Benemérita Universidad Autónoma de Puebla, México (Received 30 October 2023; accepted 13 December 2023; online 14 December 2023)

Three B2-type intermetallic AlFe_{1 – δ} phases (0.18 < δ < 0.05) in the Al–Fe binary system were synthesized by smelting and high temperature sintering methods. The exact crystal structure for δ = 0.05 was refined by single-crystal X-ray diffraction. The amount of vacancy defects at the Fe atom sites was obtained by refining the corresponding site occupancy factor, converging to the chemical formula AlFe_0.95, with a structure identical to that of ideal AlFe models inferred from powder X-ray or neutron diffraction patterns.

Keywords: crystal structure; B2 phase; Al–Fe system; vacancy.

CCDC reference: 2314099

Structure description

There are diverse intermetallic phases in the Al–Fe system, among which AlFe has attracted much attention because of its special B2 structure. For example, Van der Kraan & Buschow (1986 ) studied the crystal structure of the AlFe phase, after heat treatment at 1273 K for 50 h, by X-ray powder diffraction. The authors suggested that AlFe has a CsCl-type structure with cell parameter a = 2.907 Å. During the study of the crystal structure of La(T,Al)₁₃ (T = Fe, Co), a coexisting AlFe cubic phase was discovered. The crystal structure of cubic AlFe was also refined using X-ray powder diffraction data, affording the cell parameter a = 2.889 (4) Å, and a model in which Al and Fe atoms are occupying the Wyckoff positions 1a and 1b, respectively, in space group Pm $[\overline{3}]$ m (Guo et al., 1997 ). Makhlouf et al. (1994 ) studied the structure of the magnetic alloys FeAl_{1 - x}Rh_x by X-ray diffraction, and concluded that the crystal structure of these alloys remains in the B2 structural type. Stein et al. (2010 ), using the high-temperature neutron diffraction approach, found that the cell parameter of the AlFe phase gradually increases by increasing the temperature: the cell parameter of the AlFe phase at room temperature, 373, 1353 and 1393 K, is 2.9097, 2.9136, 2.9681 and 2.9720 Å, respectively. They also proposed that the AlFe phase has a B2-type crystal structure (Pm $[\overline{3}]$ m space group, cP2 Pearson symbol).

In the present work, three kinds of Fe-deficient B2-type AlFe_1–δ phases were synthesized by smelting and high-temperature sintering methods, with very similar lattice parameters. The AlFe_0.95 (δ = 0.05) phase was obtained by the smelting method, while AlFe_0.82 and AlFe_0.84 phases (δ = 0.18 and δ = 0.16) were obtained from an intergrowth sample by the high-temperature sintering method. The refined chemical formula of the AlFe_0.95 phase is in accordance with the complementary EDX results (see Table S1 of the supporting information). Different options for refinements are listed in Table S2 of the supporting information. The structure description reported herein is for the AlFe_0.95 (δ = 0.05) phase.

Fig. 1 shows the unit cell of AlFe_0.95. The environments of the Al and Fe sites are shown in Figs. 2 and 3, respectively. The Al1 atom at (0, 0, 0) is centred at a rhombic dodecahedron, whose vertices are six Al1 atoms and eight Fe1 atoms; conversely, the Fe1 site at (1/2, 1/2, 1/2) is surrounded by eight Al1 atoms and six Fe1 atoms. The shortest Al1 to Fe1 separation is 2.5164 (4) Å and the shortest Al1 to Al1 link is 2.9057 (5) Å. The R₁ refinement residue versus δ values has been plotted for 0 < δ < 0.1 and is shown in Fig. 4, where one can see that R₁ has the lowest value when the chemical occupancy of Fe atoms is 0.95.

Figure 1
The AlFe_0.95 structure (one unit cell), with displacement ellipsoids at the 95% probability level.

Figure 2
(a) The dodecahedron formed around the Al1 atom at the 1a site and (b) the environment of the Al1 atom with displacement ellipsoids given at the 99% probability level. [Symmetry codes: (iii) x, y, z + 1; (viii) x, y, z − 1; (ix) x − 1, y, z; (x) x, y − 1, z.]

Figure 3
(a) The dodecahedron formed around the Fe1 atom at the 1b site and (b) the environment of the Fe1 atom with displacement ellipsoids given at the 99% probability level. [Symmetry codes: (i) x + 1, y + 1, z + 1; (ii) x + 1, y, z + 1; (iii) x, y, z + 1; (iv) x + 1, y + 1, z; (v) x, y + 1, z; (vi) x, y + 1, z + 1; (vii) x + 1, y, z; (viii) x, y, z − 1; (ix) x − 1, y, z.]

Figure 4
The variation of residual R₁ versus δ for the title compound, obtained by refining the model with different values for δ. The minimum of the curve is at δ = 0.05.

Synthesis and crystallization

For the here reported sample obtained by smelting (δ = 0.05), high-purity elements Al (indicated purity 99.95%; 1.629 g) and Fe (indicated purity 99.99%; 3.371 g) were mixed in the stoichiometric ratio 1:1 and the alloy was prepared from the elements by arc melting under an argon atmosphere. Suitable pieces of single-crystal grains were broken and selected from the product for single-crystal X-ray diffraction.

For the sample obtained by high-temperature sintering (δ = 0.16 and 0.18), high-purity elements Al (indicated purity 99.95%; 0.7362 g) and Fe (indicated purity 99.9%; 0.2684 g) were mixed in the molar ratio 85:15, ground evenly in an agate mortar, and put into a silicon glass tube, which was vacuum-sealed using a home-made sealing machine. The resulting ampoule was placed in a furnace (SG-XQL1200) and heated up to 473 K for 5 min with a heating rate of 10 K min⁻¹, and then heated up to 1373 K for 2 h with the same heating rate. Finally, the sample was slowly cooled to room temperature by turning off the furnace power. Suitable pieces of single-crystal grains were broken and selected from the product for single-crystal X-ray diffraction.

Refinement

Crystal data, data collection and structure refinement details of AlFe_0.95 are summarized in Table 1, while crystal data, data collection and structure refinement details of the AlFe_0.82 and AlFe_0.84 phases are summarized in Table S3 of the supporting information. Different options for refinement are listed in Table S2. For the AlFe_0.95 phase, the maximum and minimum residual electron densities in the final difference map are located 1.30 Å and 0.72 Å from Al1.

Table 1
Experimental details

Crystal data
Chemical formula	AlFe_0.95
M_r	80.04
Crystal system, space group	Cubic, Pm $[\overline{3}]$ m
Temperature (K)	300
a (Å)	2.9057 (5)
V (Å³)	24.53 (1)
Z	1
Radiation type	Mo Kα
μ (mm⁻¹)	14.45
Crystal size (mm)	0.10 × 0.08 × 0.06

Data collection
Diffractometer	Bruker D8 Venture Photon 100 CMOS
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.560, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	815, 17, 17
R_int	0.032
(sin θ/λ)_max (Å⁻¹)	0.709

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.010, 0.026, 1.44
No. of reflections	17
No. of parameters	3
Δρ_max, Δρ_min (e Å⁻³)	0.14, −0.24
Computer programs: APEX3 and SAINT (Bruker, 2015 ), SHELXT2014/5 (Sheldrick, 2015a ), SHELXL2016/6 (Sheldrick, 2015b ), DIAMOND (Brandenburg & Putz, 2017 ), Mercury (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2314099

Crystal structure: contains datablocks I, general. DOI: https://doi.org/10.1107/S2414314623010659/bh4081sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314623010659/bh4081Isup2.hkl

ESI. DOI: https://doi.org/10.1107/S2414314623010659/bh4081sup3.docx

checkCIF report

Computing details top

Aluminium iron top

Crystal data top

AlFe_0.95	Mo Kα radiation, λ = 0.71073 Å
M_r = 80.04	Cell parameters from 750 reflections
Cubic, Pm3m	θ = 7.0–30.3°
a = 2.9057 (5) Å	µ = 14.45 mm⁻¹
V = 24.53 (1) Å³	T = 300 K
Z = 1	Lump, dark gray
F(000) = 38	0.10 × 0.08 × 0.06 mm
D_x = 5.417 Mg m⁻³

Data collection top

Bruker D8 Venture Photon 100 CMOS diffractometer	17 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.032
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 30.3°, θ_min = 7.0°
T_min = 0.560, T_max = 0.746	h = −4→4
815 measured reflections	k = −4→4
17 independent reflections	l = −4→4

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.010	w = 1/[σ²(F_o²) + (0.0141P)² + 0.007P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.026	(Δ/σ)_max < 0.001
S = 1.44	Δρ_max = 0.14 e Å⁻³
17 reflections	Δρ_min = −0.23 e Å⁻³
3 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Fe1	0.500000	0.500000	0.500000	0.0084 (3)	0.9499
Al1	0.000000	0.000000	0.000000	0.0086 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Fe1	0.0084 (3)	0.0084 (3)	0.0084 (3)	0.000	0.000	0.000
Al1	0.0086 (4)	0.0086 (4)	0.0086 (4)	0.000	0.000	0.000

Geometric parameters (Å, º) top

Fe1—Al1ⁱ	2.5164 (4)	Fe1—Fe1^viii	2.9057 (5)
Fe1—Al1	2.5164 (4)	Fe1—Fe1^v	2.9057 (5)
Fe1—Al1ⁱⁱ	2.5164 (4)	Fe1—Fe1^vii	2.9057 (5)
Fe1—Al1ⁱⁱⁱ	2.5164 (4)	Fe1—Fe1^ix	2.9057 (5)
Fe1—Al1^iv	2.5164 (4)	Al1—Al1ⁱⁱⁱ	2.9057 (5)
Fe1—Al1^v	2.5164 (4)	Al1—Al1^viii	2.9057 (5)
Fe1—Al1^vi	2.5164 (4)	Al1—Al1^x	2.9057 (5)
Fe1—Al1^vii	2.5164 (4)	Al1—Al1^ix	2.9057 (5)

Al1ⁱ—Fe1—Al1	180.0	Fe1^xi—Al1—Fe1	180.0
Al1ⁱ—Fe1—Al1ⁱⁱ	70.5	Fe1^xi—Al1—Fe1^x	109.5
Al1—Fe1—Al1ⁱⁱ	109.5	Fe1—Al1—Fe1^x	70.5
Al1ⁱ—Fe1—Al1ⁱⁱⁱ	109.5	Fe1^xi—Al1—Fe1^xii	70.5
Al1—Fe1—Al1ⁱⁱⁱ	70.529 (1)	Fe1—Al1—Fe1^xii	109.5
Al1ⁱⁱ—Fe1—Al1ⁱⁱⁱ	70.5	Fe1^x—Al1—Fe1^xii	70.5
Al1ⁱ—Fe1—Al1^iv	70.529 (1)	Fe1^xi—Al1—Fe1^xiii	70.5
Al1—Fe1—Al1^iv	109.471 (1)	Fe1—Al1—Fe1^xiii	109.5
Al1ⁱⁱ—Fe1—Al1^iv	109.5	Fe1^x—Al1—Fe1^xiii	180.0
Al1ⁱⁱⁱ—Fe1—Al1^iv	180.0	Fe1^xii—Al1—Fe1^xiii	109.5
Al1ⁱ—Fe1—Al1^v	109.5	Fe1^xi—Al1—Fe1^viii	109.5
Al1—Fe1—Al1^v	70.5	Fe1—Al1—Fe1^viii	70.5
Al1ⁱⁱ—Fe1—Al1^v	180.0	Fe1^x—Al1—Fe1^viii	109.5
Al1ⁱⁱⁱ—Fe1—Al1^v	109.5	Fe1^xii—Al1—Fe1^viii	180.0
Al1^iv—Fe1—Al1^v	70.5	Fe1^xiii—Al1—Fe1^viii	70.5
Al1ⁱ—Fe1—Al1^vi	70.529 (1)	Fe1^xi—Al1—Fe1^ix	109.5
Al1—Fe1—Al1^vi	109.471 (1)	Fe1—Al1—Fe1^ix	70.5
Al1ⁱⁱ—Fe1—Al1^vi	109.5	Fe1^x—Al1—Fe1^ix	109.5
Al1ⁱⁱⁱ—Fe1—Al1^vi	70.5	Fe1^xii—Al1—Fe1^ix	70.5
Al1^iv—Fe1—Al1^vi	109.5	Fe1^xiii—Al1—Fe1^ix	70.5
Al1^v—Fe1—Al1^vi	70.5	Fe1^viii—Al1—Fe1^ix	109.5
Al1ⁱ—Fe1—Al1^vii	109.5	Fe1^xi—Al1—Fe1^xiv	70.5
Al1—Fe1—Al1^vii	70.5	Fe1—Al1—Fe1^xiv	109.5
Al1ⁱⁱ—Fe1—Al1^vii	70.5	Fe1^x—Al1—Fe1^xiv	70.5
Al1ⁱⁱⁱ—Fe1—Al1^vii	109.5	Fe1^xii—Al1—Fe1^xiv	109.5
Al1^iv—Fe1—Al1^vii	70.5	Fe1^xiii—Al1—Fe1^xiv	109.5
Al1^v—Fe1—Al1^vii	109.5	Fe1^viii—Al1—Fe1^xiv	70.5
Al1^vi—Fe1—Al1^vii	180.0	Fe1^ix—Al1—Fe1^xiv	180.0
Al1ⁱ—Fe1—Fe1^viii	125.3	Fe1^xi—Al1—Al1ⁱⁱⁱ	125.3
Al1—Fe1—Fe1^viii	54.7	Fe1—Al1—Al1ⁱⁱⁱ	54.7
Al1ⁱⁱ—Fe1—Fe1^viii	125.3	Fe1^x—Al1—Al1ⁱⁱⁱ	54.7
Al1ⁱⁱⁱ—Fe1—Fe1^viii	125.3	Fe1^xii—Al1—Al1ⁱⁱⁱ	54.7
Al1^iv—Fe1—Fe1^viii	54.7	Fe1^xiii—Al1—Al1ⁱⁱⁱ	125.3
Al1^v—Fe1—Fe1^viii	54.7	Fe1^viii—Al1—Al1ⁱⁱⁱ	125.3
Al1^vi—Fe1—Fe1^viii	125.3	Fe1^ix—Al1—Al1ⁱⁱⁱ	54.7
Al1^vii—Fe1—Fe1^viii	54.7	Fe1^xiv—Al1—Al1ⁱⁱⁱ	125.3
Al1ⁱ—Fe1—Fe1^v	54.7	Fe1^xi—Al1—Al1^viii	54.7
Al1—Fe1—Fe1^v	125.3	Fe1—Al1—Al1^viii	125.3
Al1ⁱⁱ—Fe1—Fe1^v	125.3	Fe1^x—Al1—Al1^viii	125.3
Al1ⁱⁱⁱ—Fe1—Fe1^v	125.3	Fe1^xii—Al1—Al1^viii	125.3
Al1^iv—Fe1—Fe1^v	54.7	Fe1^xiii—Al1—Al1^viii	54.7
Al1^v—Fe1—Fe1^v	54.7	Fe1^viii—Al1—Al1^viii	54.7
Al1^vi—Fe1—Fe1^v	54.7	Fe1^ix—Al1—Al1^viii	125.3
Al1^vii—Fe1—Fe1^v	125.3	Fe1^xiv—Al1—Al1^viii	54.7
Fe1^viii—Fe1—Fe1^v	90.0	Al1ⁱⁱⁱ—Al1—Al1^viii	180.0
Al1ⁱ—Fe1—Fe1^vii	54.7	Fe1^xi—Al1—Al1^x	54.7
Al1—Fe1—Fe1^vii	125.3	Fe1—Al1—Al1^x	125.3
Al1ⁱⁱ—Fe1—Fe1^vii	54.7	Fe1^x—Al1—Al1^x	54.7
Al1ⁱⁱⁱ—Fe1—Fe1^vii	125.3	Fe1^xii—Al1—Al1^x	54.7
Al1^iv—Fe1—Fe1^vii	54.7	Fe1^xiii—Al1—Al1^x	125.3
Al1^v—Fe1—Fe1^vii	125.3	Fe1^viii—Al1—Al1^x	125.3
Al1^vi—Fe1—Fe1^vii	125.3	Fe1^ix—Al1—Al1^x	125.3
Al1^vii—Fe1—Fe1^vii	54.7	Fe1^xiv—Al1—Al1^x	54.7
Fe1^viii—Fe1—Fe1^vii	90.0	Al1ⁱⁱⁱ—Al1—Al1^x	90.0
Fe1^v—Fe1—Fe1^vii	90.0	Al1^viii—Al1—Al1^x	90.0
Al1ⁱ—Fe1—Fe1^ix	125.3	Fe1^xi—Al1—Al1^ix	54.7
Al1—Fe1—Fe1^ix	54.7	Fe1—Al1—Al1^ix	125.3
Al1ⁱⁱ—Fe1—Fe1^ix	125.3	Fe1^x—Al1—Al1^ix	125.3
Al1ⁱⁱⁱ—Fe1—Fe1^ix	54.7	Fe1^xii—Al1—Al1^ix	54.7
Al1^iv—Fe1—Fe1^ix	125.3	Fe1^xiii—Al1—Al1^ix	54.7
Al1^v—Fe1—Fe1^ix	54.7	Fe1^viii—Al1—Al1^ix	125.3
Al1^vi—Fe1—Fe1^ix	54.7	Fe1^ix—Al1—Al1^ix	54.7
Al1^vii—Fe1—Fe1^ix	125.3	Fe1^xiv—Al1—Al1^ix	125.3
Fe1^viii—Fe1—Fe1^ix	90.0	Al1ⁱⁱⁱ—Al1—Al1^ix	90.0
Fe1^v—Fe1—Fe1^ix	90.0	Al1^viii—Al1—Al1^ix	90.0
Fe1^vii—Fe1—Fe1^ix	180.0	Al1^x—Al1—Al1^ix	90.0

Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1, y, z+1; (iii) x, y, z+1; (iv) x+1, y+1, z; (v) x, y+1, z; (vi) x, y+1, z+1; (vii) x+1, y, z; (viii) x, y, z−1; (ix) x−1, y, z; (x) x, y−1, z; (xi) x−1, y−1, z−1; (xii) x−1, y−1, z; (xiii) x−1, y, z−1; (xiv) x, y−1, z−1.

Funding information

Funding for this research was provided by: The National Natural Science Foundation of China (grant Nos. 52173231 and 51925105); Hebei Natural Science Foundation (grant No. E2022203182); The Innovation Ability Promotion Project of Hebei supported by Hebei Key Lab for Optimizing Metal Product Technology and Performance (grant No. 22567609H).

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