Synthesis, crystal structure and physical properties of a novel quaternary selenide Cu6GeWSe8

Abstract

Here we report a novel quaternary selenide Cu6GeWSe8 synthesized directly from the constituent elements, which forms within the temperature range from 460 to 620 ​°C. It crystallizes in the space group P63mc with two formula units in the cell of dimensions a ​= ​7.8651 (5) Å, c ​= ​12.9275 (6) Å. In the unit cell composed of MSe4 (M ​= ​Cu, Ge and W) tetrahedrons, Cu atoms occupy two sets of 6c Wyckoff positions, Ge and W atoms respectively occupy 2a and 2b positions, while Se atoms are located at four inequivalent sites, respectively 2b (Se1), 6c (Se2), 6c (Se3) and 2a (Se4). The electrical resistivity and Vis-Nir absorption spectrum indicate that the compound exhibits a semiconducting behavior with an optical band gap of 1.586 ​eV Cu6GeWSe8 shows diamagnetism at room temperature and the emergence of a Curie-Weiss-like tail at low temperature. The band structure calculation demonstrates that the title compound has a direct band gap, and Cu and Se atoms dominantly contribute to the energy bands and density of states. Cu is mostly in 3d10 state (+1 valence) and Se in 4p6 state (−2 valence). On the basis of the experimental and calculation results, it is concluded that Cu6GeWSe8 is a diamagnetic direct-gap semiconductor.