title: Dicalcium heptagermanate Ca(2)Ge(7)O(16) revised.
abstract: The structure of dicalcium heptagermanate, previously described with an orthorhombic space group, has been redetermined in the tetragonal space group P(overline4)b2. It contains three Ge positions (site symmetry 1, ..2 and 2.22, respectively), one Ca position (..2) and four O atoms, all on general 8i positions (site symmetry 1). A sheet of four-membered rings of Ge tetrahedra (with Ge on the 8i position) and isolated Ge tetrahedra (Ge on the 4g position) alternate with a sheet of Ge octahedra (Ge on the 2d position) and eightfold-coordinated Ca sites along the c direction in an ABABA... sequence. The three-dimensional framework of Ge sites displays a channel-like structure, evident in a projection on to the ab plane.
authors.affiliation: Department of Materials Engineering and Physics, Division of Mineralogy, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria. guenther.redhammer@aon.at
authors.forename: Günther J
authors.initials: GJ
authors.lastname: Redhammer
authors.forename: Georg
authors.initials: G
authors.lastname: Roth
authors.forename: Georg
authors.initials: G
authors.lastname: Amthauer