Crystal structure of Yb2CuGe6 and Yb3Cu4Ge4 and the valency of ytterbium

Abstract

The Yb2CuGe6 and Yb3Cu4Ge4 compounds were synthesized from reaction mixtures using indium as flux. Both powder and single crystal X-ray diffraction data were used to refine the crystal structures. Yb2CuGe6 crystallizes in the monoclinic space group C2/m in the La2AlGe6 type structure. The lattice parameters are a = 8.0011(16) angstrom, b = 8.1962(16) angstrom, c = 10.682(2) angstrom and beta = 100.63(3). The crystal structure of Yb2CuGe6 can be described as the intergrowth of fragments Ge dimmers and zig-zag Ge chains. Yb3Cu4Ge4 crystallizes in the orthorhombic space group Immm in the Gd3Cu4Ge4 type structure. The lattice parameters are a = 4.1302(8) angstrom, b = 6.5985(13) angstrom and c = 13.691(3) angstrom. X-ray absorption near edge spectroscopy (XANES) measurements indicate that Yb in Yb2CuGe6 and Yb3Cu4Ge4 exists as intermediate and trivalent states, respectively. The structural refinement of Yb2CuGe6 is corroborated by total energy calculations within the local density approximation. (C) 2013 Elsevier B.V. All rights reserved.