Crystal structure of the ternary compound Sc₃Cu_7.5Al_7.5

Chem. Met. Alloys 9 (2016) 78-83

https://doi.org/10.30970/cma9.0348

Nastasia KLYMENTIY, Nataliya SEMUSO, Svitlana PUKAS, Yaroslav TOKAYCHUK, Lev AKSELRUD, Roman GLADYSHEVSKII

The crystal structure of a new ternary aluminide, Sc₃Cu_7.5Al_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 Sc₃Ni₁₁Ge₄ (Pearson symbol hP38, space group P6₃/mmc, a = 8.4848(1), c = 8.8593(1) Å). The hexagonal unit cell of Sc₃Cu_7.5Al_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.

Projection of the unit cell of the structure of the compound Sc₃Cu_7.5Al_7.5 along the crystallographic direction [001].

Keywords

Aluminum / Copper / Scandium / X-ray powder diffraction / Crystal structure / Rare-earth atom triangles