New Barium Copper Chalcogenides Synthesized Using Two Different Chalcogen Atoms: Ba₂Cu_6–<i>x</i>STe₄ and Ba₂Cu_6–<i>x</i>Se_<i>y</i>Te_5–<i>y</i>

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.