Mixed crystals in the system Cu2MnGexSnl-xS4:: Phase analytical investigations and inspection of tetrahedra volumes

Cu2MnGeS4 crystallizes orthorhombic in a wurtzite superstructure type while Cu2MnSnS4 crystallizes in a tetragonal sphalerite superstructure type. Lattice constants and thermal analyses of the solid solution series Cu2MnGexSn1-xS4 are presented. A two-phase region is found from Cu2MnGe0.3Sn0.7S4 to Cu2MnGe0.5Sn0.5S4. The cell volume of the mixed crystals increases with increasing Sri content. The melting points increase smoothly with increasing Ge content to x = 0.5 and then steeply for higher Ge contents. The single crystal X-ray structure analysis Of Cu2MnGe0.55Sn045S4 is presented. The refinement converges to R = 0.0270 and wR(2) = 0.0586, Z is 2. The volumes of the tetrahedra [MS4] (M = Cu, Mn, Ge, Sn) are calculated. From these volumes the differences in size of the tetrahedra are derived and compared with the corresponding differences in the end members of the solid solution series. It turns out that the resulting structure type in these materials depends on the volume differences of the constituting tetrahedra [MS4]. (C) 2005 Elsevier Inc. All rights reserved.