The structure of decagonal Al70.5Mn16.5Pd13

The structure of the stable decagonal quasicrystal Al 70.5 Mn 16.5 Pd 13 was determined by single-crystal X-ray methods. Higher-dimensional structure-solution techniques were employed, such as five-dimensional (5D) Patterson and Fourier syntheses as well as 5D least-squares structure refinements. A 3D physical-space maximum-entropy method (MEM) was used in the course of structure-factor phasing and for the calculation of a high-quality electron-density distribution function. Geometrically, the structure may be described as a periodic stacking of two different quasiperiodic layers A (puckered +or-0.3 AA) and B (planar) with sequence ABAaba (a and b denote the layers A and B, respectively, rotated by 2 pi /10), consistent with the centrosymmetric 5D superspace group P10 5 /mmc. Basic structure-building elements, however, are columnar clusters (OE approximately 20 AA) with cross-sections corresponding to parts of a decorated Penrose tiling. The clusters are packed in a way that results in a disordered Robinson-triangle tiling. The title compound is isotypic to metastable decagonal Al 78 Mn 22 and locally shows a strong resemblance to icosahedral Al 68.7 Mn 9.6 Pd 21.7 , orthorhombic Al 3 Mn and hexagonal mu -Al 4.12Mn.