Crystal structure of the ternary compound Sc3Cu7.5Al7.5

Abstract

The crystal structure of a new ternary aluminide, Sc 3 Cu 7.5 Al 7.5 , was solved by direct methods from X-ray powder diffraction data. It crystallizes with a partly disordered occupation variant of the structure type Sc 3 Ni 11 Ge 4 (Pearson symbol hP38, space group P6 3 /mmc, a = 8.4848(1), c = 8.8593(1) Å). The hexagonal unit cell of Sc 3 Cu 7.5 Al 7.5 contains 36 atoms, distributed over seven crystallographic sites (Sc atoms: one site, statistical mixtures of Cu and Al atoms: four sites, Cu atoms alone: two partly occupied sites). The main feature of the structure is the clustering of the Sc atoms into triangles with relatively short interatomic distances (δ Sc-Sc = 3.446(2) Å). The coordination polyhedra of the Sc atoms are pentagonal prisms (with seven capping atoms) and those of the sites occupied by atoms of the statistical mixtures icosahedra, and those of the remaining Cu atoms trigonal prisms (with three capping atoms) or trigonal antiprisms.

The Ternary Systems {Sc, Ti}-Cu-Al at 800°C

“…The existence of two, four, and three binary compounds at this temperature was confirmed in the Sc-Cu, Sc-Al, and Cu-Al system, respectively: ScCu Six ternary compounds were confirmed in the Sc-Cu-Al system: ScCu 4.9-6.0 Al 7.1-6.0 , Sc 2 Cu 6.25 Al 4.75 , ScCu 2 Al, ScCu 0.6 Al 1.4 , ScCuAl, and Sc 0.5 CuAl 0.5 . The existence of two new ternary compounds, Sc 6 Cu 24.1 Al 11.9 and Sc 3 Cu 7.5 Al 7.5 was already reported in [7,8], and the formation of a continuous solid solution ScCu 1-x Al x (x = 0-1) based on the binary compounds ScCu and ScAl with CsCl-type structure in [9]. Unit-cell parameters of the above mentioned compounds are listed in Table 1.…”

“…The authors of [5] confirmed the existence of the compound Sc 2 Cu 6.25 Al 4.75 (oS108, Cmmm), the composition of which was previously given as Sc 3 Cu 9 Al 7 . Three more compounds form in the system Sc-Cu-Al, two of them with own structure types: Sc 3 Cu 6.8 Al 9.2 (hP38, P6 3 /mmc) [6], Sc 6 Cu 24.1 Al 11.9 (cI176, Im-3, a = 13.5337 Å) [7], and Sc 3 Cu 7.5 Al 7.5 (Sc 3 Ni 11 Ge 4 , hP38, P6 3 /mmc, a = 8.4848, c = 8.8593 Å) [8]. The existence of a continuous solid solution ScCu 1-x Al x (x = 0-1), based on the binary compounds ScCu and ScAl with CsCl-type structure (cP2, Pm-3m), was established [9].…”