New Barium Copper Chalcogenides Synthesized Using Two Different Chalcogen Atoms: Ba2Cu6–xSTe4 and Ba2Cu6–xSeyTe5–y

Ba2Cu6–xSTe4 and Ba2Cu6–xSeyTe5–y were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) Å, b = 14.0533(9) Å, c = 4.3524(3) Å, and V = 590.61(7) Å3 in the case of Ba2Cu5.53(3)STe4. A significant phase width was observed in the case of Ba2Cu6–xSeyTe5–y with at least 0.17(3) ≤ x ≤ 0.57(4) and 0.48(1) ≤ y ≤ 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba2Cu6–xSTe4, Cu–Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba2Cu6–xSeyTe5–y, the bridging atom is either a Se atom or a Se/Te mixture when y ≤ 1, and the Te atoms of the Cu–Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba2+, Cu+, S2–, Se2–, and Te2–. Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples.