On the crystal structure of the Mn-Ni-Si G-phase

The crystal structure of Mn6Ni16Si7 was reinvestigated by X-ray powder, single crystal and neutron powder diffraction data inform of a combined refinement. In contrast to the various structure variants observed for titanium aluminium-based G-phases Ti-6({Fe,Co,Ni}(1-x)Al-x)(23+1) as well as for Ti6Ni16+xSi7, Mn6Ni16Si7 was confirmed to crystallize as a simple ordered variant of the Th6Mn23 structure type (a = 1.11674(6) nm, Mg6Cu16Si7-type; space group Fm (3) over barm): Ni atoms adopt two 32f sites, Si atoms occupy 4a and 24d sites and Mn-atoms are located at 24e sites. A Fourier difference map proved the absence of atoms in the 4b site (1/2, 1/2, 1/2). Thus the crystal structure of Mn6Ni16Si7 is a true representative of the Mg6Cu16Si7-type. (C) 2008 Elsevier B.V. All rights reserved.