The crystal structure of the metallic phase Mg32(Al, Zn)49

Abstract

A complete determination of the crystal structure of the ternary phase (~t or T phase) in the magnesium-aluminum-zinc system with composition approximately MgaZnaAI 2 has been carried out with use of intensity data from single-crystal Weissenberg photographs. The refinement of the structural parameters was carried out by use of Fourier projections, followed by application of the method of least squares. The unit of structure, based on the body-centered cubic lattice, has a 0 ----14.16 ~, as previously reported by Laves, L6hberg & Witte. The space group is T~, with 162 atoms per unit cube. The structtLre shows the correct formula to be Mg32(A1 , Zn)49; there is some disorder in occupancy of positions by aluminum and zinc atoms. The icosahedron and truncated tetrahedron are prominent coordination polyhedra in this structure.

A crystal-chemical model of atomic interactions. 5. Quasicrystal structures

“…The main result of these two refinements was the interchange of positions of one of the lithium atoms with one of the aluminium atoms. Also, the paper by De Boissien et al (1989) insisted that the twofold position, denoted A by Bergman, Waugh & Pauling (1957), was vacant, but, as will be shown below, this fact is not important for the point of view under consideration.…”

“…Taking into account the fact that both aluminium and copper atoms are placed together at the same positions, we designate five independent aluminium and copper atoms distributed at G, A, B, C and F positions (Bergman, Waugh & Pauling, 1957) by symbols A1-AS, respectively. For brevity the lithium atoms are marked by symbols L1-L3; these atoms are distributed at D, E and H positions.…”

Complex Metallic Alloys

“…Inside the giant unit cells a cluster substructure exists. For example, there is a large group of alloys based on the 55 atom Mackay icosahedron, another group is based on the 105 atom Bergman cluster [4]. Today hundreds of such compounds are known whose structures are based on giant unit cells [5].…”

Characterisation of Quasicrystalline Particles in an Isothermally Aged Al–10Mg–0.5Ag (mass%) Alloy

“…13) Great progress on understanding of the structure of icosahedral quasicrystalline phases was made by recognising 14,15) that there are two major classes of icosahedral quasicrystals, i.e. Mackay icosahedral clusters in Al-Mn and Al-Mn-Si 16) alloys and Pauling triacontahedral clusters in Mg-Al-Zn 4) and Al-Cu-Li alloys.…”

“…2) Wheeler et al 3) proposed that peak hardness in the ternary Al-Mg-Ag alloy can be associated with fine scale precipitates of the T phase, Mg 32 (Al,Ag) 49 (space group Im 3 3, body-centred cubic structure, a ¼ 1:416 nm), 4) rather than precipitation of the phase, Al 3 Mg 2 (space group Fd 3 3m, face-centred cubic structure, a ¼ 2:824 nm). 5,6) Auld 7) determined the orientation relationship between the matrix and precipitates of the T phase by X-ray diffraction technique; ð100Þ T k ð112Þ , ½001 T k ½110 .…”