The crystal structure of the ternary alloy c-Al₆₈Pd₂₀Ru₁₂

Abstract

The crystal structure of cubic Al₆₈Pd₂₀Ru₁₂ was investigated by means of single crystal X-ray structure analysis: space group P23 (No. 195), a = 15.540(2) Å, V = 3753(1) ų, Pearson symbol cP296–46.85. The chemical composition was determined by microprobe analysis: Al₆₈Pd₂₀Ru₁₂, M_r = 6316, Z = 2, D_calc = 5.59 Mg m⁻³; MoK_α, refined as Al₈₇Pd₃₈, F(000) = 5758, μ = 9.89 mm⁻¹, R(wR) = 0.056(0.052) for 1289 reflections with F > 3σ(F) and 133 variables, goodness of fit S = 2.21. The structure contains 35 different orbits. Body centred pseudo symmetry is broken by the distribution of atoms, the non-centrosymmetric point symmetry 23 of this structure is close to m[unk] in space group Pn[unk]. Disorder of Al atoms is observed at a number of positions. Interatomic distances cover the ranges of 2.98 Å to 3.20 Å, 2.43 Å to 3.12 Å and 2.54 Å to 3.66 Å, for contacts TM–TM, Al–TM and Al–Al, respectively (TM: transition metal). The coordination shells contain triangular and/or quadrangular faces forming icosahedra, rhombic dodecahedra or respective combinations of these two basic forms. Links to cubic approximants of icosahedral phases are shown and relationships to neighboring crystalline and decagonal phases are discussed.