Crystal structure of a 2/1 cubic approximant in an Al–Rh–Si alloy

The structure of a cubic Al66.5Rh26.1Si7.3 phase, which is referred as a 2/1 approximant for an icosahedral phase, was determined by means of single crystal X-ray structural analysis: space group Pm3, a=19.935(2) Å, Mo Kα (λ=0.71069 Å); refined as Al70.4Rh29.6, R(wR2)=0.087(0.194) for 1391 reflections with I>2.0σ(I). A dodecahedral atom cluster is located at the origin of a unit cell, and the corresponding atomic arrangement can be described as nine shells with a local icosahedral symmetry, by suggesting a close similarity to the dodecahedral atomic cluster of the 2/1-AlPdMnSi approximant. The 2/1-AlRhSi approximant is a second example of a simple cubic arrangement of dodecahedral atom clusters that are 20 Å in diameter.