Preparation and crystal structure of the novel decagonal approximant Mn123Ga137

A new approximant to a decagonal quasicrystal has been found in the Ga-Mn binary system. Single crystals of Mn123Ga137 were synthesised from pieces of manganese in a self flux of gallium. Still at the reaction temperature, the liquid flux and the solid Mn123Ga137 crystals weir separated from each other by centrifugal action filtering. The crystal structure of Mn123Ga137 was determined from single crystal X-ray diffraction data. Mn123Ga137 crystallises in the monoclinic space group C2/c, a = 20.239(3) Angstrom, b = 14.790(2) Angstrom, 14.908(2) Angstrom, beta = 120.93(2)degrees, R-w = 4.0%. The structure consist mainly of a fundamental type of wheel shaped pentagonal clusters with 5/mm point group pseudo symmetry. The cluster consists of seven intergrown icosahedra. Each cluster is fused to three other in the plane perpendicular to the pseudo five-fold axis. In that way they make up infinite honeycomb nets parallel to the a-b plane. (C) 2001 Elsevier Science B.V. All rights reserved.