Mixed crystals in the system Cu2MnGexSn1−xS4: Phase analytical investigations and inspection of tetrahedra volumes

Abstract

Cu 2 MnGeS 4 crystallizes orthorhombic in a wurtzite superstructure type while Cu 2 MnSnS 4 crystallizes in a tetragonal sphalerite superstructure type. Lattice constants and thermal analyses of the solid solution series Cu 2 MnGe x Sn 1Àx S 4 are presented. A two-phase region is found from Cu 2 MnGe 0.3 Sn 0.7 S 4 to Cu 2 MnGe 0.5 Sn 0.5 S 4 . The cell volume of the mixed crystals increases with increasing Sn content. The melting points increase smoothly with increasing Ge content to x ¼ 0:5 and then steeply for higher Ge contents. The single crystal X-ray structure analysis of Cu 2 MnGe 0.55 Sn 0.45 S 4 is presented. The refinement converges to R ¼ 0:0270 and wR 2 ¼ 0:0586, Z is 2. The volumes of the tetrahedra [MS 4 ] (M ¼ 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 [MS 4 ].

The Ag2S–In2S3–Si(Ge)S2 systems and crystal structure of quaternary sulfides Ag2In2Si(Ge)S6

“…Such an approach was used in Refs. [67,68]; it is used for the tetrahedral compounds exclusively [69]. Cadmium in ternary compounds has the size intermediate between that of Ag and In.…”

Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes

“…Compounds with M IV ϭ Ge cannot be associated preferentially to one of both structure types [9]. Therefore we investigated mixed crystals in the system Cu 2 MnGeS 4 (wurtzstannite) Ϫ Cu 2 MnSnS 4 (stannite) for a better understanding of the influence of the M IV -cation on the structure type [26]. It seems to be desirable to check also the influence of the M II -cation.…”

“…on the influence of variation on the position of the divalent cation. We present mixed crystals in the system Cu 2 Mn x Co 1Ϫx GeS 4 (0 < x < 1) and compare the tetrahedra volumes with those described in [25] and [26].…”

“…We expect our concept to be more applicable as it is based on experimental structural data instead of empirical averaged data. Averaging data can lead to erroneous conclusions as it becomes evident from our latest results [26]. However, both concepts are tools to reconsider the quality and correctness of older structure refinements.…”

Magnetoelectric and multiferroic properties of ternary copper chalcogenides Cu2MIIMIVS4

“…This is the case for instance for Cu 2 MnGeS 4 where the melting point has been reported to be T m = 1287 K [18].…”