Crystal structure of the b.c.o. Al4(Cr, Ni) decagonal approximant

The crystal structure of the orthorhombic Al-4(Cr,Ni) coexisting with the decagonal quasicrystal in the Al-Cr-Ni system was determined by single crystal X-ray structure analysis: Immm (No. 71), a = 1.2505 nm, b = 1.2619 nm, c = 3.0660 nm, V = 4.8382 nm(3). Pearson symbol oI366-58.16, D-x = 3.451 g/cm(3), R-1= 0.0728 for 2257 reflections, goodness of fit S = 0,954. There are 39 (28Al + 11Cr/Ni) independent atoms in a unit cell, of which four Al and nine (Cr/Ni) atoms have icosahedral coordination. As in many Al-TM (transition metal) intermetallic phases, a number of Al sites in Al,(Cr,Ni) have a partial occupancy of only 0.5-0.67. The base-centered orthorhombic Al,(Cr,Ni) consists of six layers alone, the a-axis, two flat ones each sandwiched between two puckered layers in mirror reflection. The interconnection of icosahedral clusters in this structure also exists in the hexagonal mu-Al4Mn, kappa-AlCrNi, lambda-Al4Mn and nu-Al12Cr2Fe phases. (C) 2002 Elsevier Science B.V. All rights reserved.