Crystal Structure and Physical Properties of the New Chalcogenides Ba3Cu17–x(S,Te)11 and Ba3Cu17–x(S,Te)11.5 with Two Different Cu Clusters

The sulfide-tellurides Ba3Cu17–x(S,Te)11 and Ba3Cu17–x(S,Te)11.5 were synthesized from the elements in stoichiometric ratios heated to 1073 K, followed by slow cooling to 873 K over 100 h. Ba3Cu17–x(S,Te)11 is isostructural to Ba3Cu17–x(Se,Te)11 when [S] > [Te], space group R3̅m, with lattice dimensions of a = 12.009(1) Å, c = 27.764(2) Å, V = 3467.6(5) Å3, for Ba3Cu15.7(4)S7.051(5)Te3.949 (Z = 6). The structure is composed of Cu atoms forming paired hexagonal antiprisms, capped on the two outer hexagonal faces, where each Cu atom is tetrahedrally coordinated by four Q (= S, Te) atoms. The new variant is formed when [Te] > [S]; then Ba3Cu17–x(S,Te)11.5 adopts space group Fm3̅m with a = 17.2095(8) Å, V = 5096.9(4) Å3, for Ba3Cu15.6(2)S5.33(4)Te6.17 (Z = 8). This structure consists of eight Te-centered Cu16 icosioctahedra per cell interconnected by cubic Cu8 units centered by Q atoms. Electronic structure calculations and property measurements illustrate that these compounds behave as extrinsic p-type semiconductorstoward metallic behavior for the latter compound. With standard oxidation states Ba2+, Cu+, and Q2–, the electron precise formulas are Ba3Cu16Q11 and Ba3Cu17Q11.5.