Crystal Structure and Physical Properties of the New Selenide-Tellurides Ba3Cu17-x(Se,Te)11

The selenide-tellurides Ba3Cu17-x(Se,Te)(11) were synthesized from the elements in stoichiometric ratios at 750 degrees C, followed by slow cooling. Ba3Cu17-x(Se,Te)(11) adopts a new structure type, space group R (3) over barm, with lattice dimensions of a = 12.1718(4) angstrom, c = 28.197(2) angstrom, V = 3617.8(3) angstrom(3), for Ba3Cu14.4(2)Se8.6(1)Te2.4 (Z = 6). Noticeable variations both in the copper content (e.g., 2.0 <= x <= 2.6) and Se:Te ratio (at least between 8.6:2.4 and 7.7:3.3) were observed, depending on the starting element ratios. All Cu atoms are tetrahedrally coordinated by Se and Te atoms and form a three-dimensional network via various Cu-Cu interactions. Because all Cu sites exhibit deficiencies, Ag ions can replace significant amounts of Cu under ambient conditions, proving a certain degree of ion conductivity. A small band gap was calculated for the electron precise material with x = 1, namely for the model Ba3Cu16Se8Te3. Accordingly, the materials with x > 1 are p-doped semiconductors, as confirmed via Seebeck and electrical conductivity measurements.