Crystal Structure of the Ternary Compound Sc₆Cu_24.1Al_11.9

Abstract

The crystal structure of a new ternary aluminide of refined composition Sc6Cu24.1(2)Al11.9(2) was solved by direct methods from X-ray powder diffraction data. It belongs to the cubic space group Im-3, Pearson symbol cI176-8, a = 13.5337(5) Å. The structure of Sc6Cu24.1Al11.9 may be described as a packing of 16-vertex coordination polyhedra of the Sc atoms, which form icosahedral clusters around the origin and the center of the body-centered unit cell. The voids at the centers of the clusters are filled by Cu4 tetrahedra, disordered between two possible orientations. The structure is closely related to the structure types Ru3Be17 and Ce6Au27.6Sn6.8.

Planar defect in approximant: the case of Cu-Al-Sc alloy

“…These results are consistent with the characteristics in the previous report on the 1/1 approximant [9]. Rietveld analysis was performed using the structure model [9] as the starting model belonging to the space group Im3 . Anisotropic displacement was assumed for each site in this analysis, and the atomic compositions and position parameters were modified to better fit the measured intensity distribution.…”

“…The lattice parameter was determined to be 13.523(3) Å. These results are consistent with the characteristics in the previous report on the 1/1 approximant [9]. Rietveld analysis was performed using the structure model [9] as the starting model belonging to the space group Im3 .…”

“…Tsai-type approximants are formed in many alloys as follows; Cu-, Zn-, Pd-, Ag-, Cd-, and Au-based alloys [7,8]. In this paper, a 1/1 approximant formed in Cu-Al-Sc alloy [9] is treated as an example. In this system, in addition to the 1/1 approximant, the following quasicrystal-related phases are reported; P-type icosahedral quasicrystal with a 6D =6.959 Å [10,11], orthorhombic 1/0-2/1-1/0 approximant with a=8.337 Å, b=22.02 Å, c= 8.305 Å [11,12].…”

Exploration in the Sc-Al-Cu system: evidence for i-ScAl2.4Cu3.2 quasicrystal and new crystal data for five intermetallic phases

“…Such a description has been recently given for the cubic compound ScAl1.98Cu4.02 in which Sc lies inside a 16-vertex polyhedron displaying 18 triangular, 2 square and 1 pentagonal faces [32]. Each Sc@Cu3Al(Cu/Al)12 polyhedron shares a triangular face with each of its ten neighbours so as their pentagonal faces form a dodecahedral cavity.…”

“…It should be stressed that at the moment this work was initiated, only lattice parameters were known for the orthorhombic structure characterized later [31], the structure of which has been included recently in the Pearson database (2016 update) [30]. At the same time, the new compound ScAl1.98Cu4.02 was identified from its powder pattern and its cubic Im 3 structure is described in a paper which enumerates also the older works published on this ternary system [32].…”