The structure of decagonal Al70Ni15Co15

The quasiperiodic structure of decagonal Al70Ni15Co15 was determined on the basis of X-ray single-crystal intensity data using the n-dimensional embedding method. Centrosymmetric five-dimensional space group P105/mmc, three-dimensional reciprocal and direct quasilattice parameters: ai*=0.2636(1) A-1, i=1, .., 4, a5*=0.24506(3) A-1, a1=3.794(1) A, i=1, .., 4, a5=4.0807(3) A. Five-dimensional unit-cell parameters: di=3.393(1), d5=4.0807(3) A, αij=60 , αi5=90 , i, j=1, .., 4, V=302.4 A5, Mr=36.54, Dx=4.5 Mg m-3, μ=10.1 mm-1, Mo Kα, wR=0.078, R=0.091 for 253 unique reflections and 21 variables. A five-dimensional structure model was obtained by Patterson syntheses and refined by the least-squares technique. High-resolution electron-density maps were calculated by the maximum-entropy method. The structure is formally built up by two quasiperiodic atomic layers with stacking sequence Aa (a denotes the layer A rotated around 2π/10). It is essentially isotypic to that od decagonal Al65Cu20Co15 and shows locally a close resemblance to monoclinic Al13Co4. Columnar clusters parallel to the loca tenfold screw axes, formed by ten pentagonal antiprismatic columns surrounding a central column, are found to be the basic structural building elements. Quasiperiodicity is forced by the formation of interconnected networks of closed icosagonal rings of pentagonal and rectangular structure motifs. (orig.)