Thermoelectric properties of the new polytelluride Ba3Cu14-δTe12

Ba3Cu14-delta Te-12 was prepared by directly reacting the elements in stoichiometric ratios at 800 degrees C for 3 days, followed by slow cooling. Ba3Cu14-delta Te12 forms a new structure type, space group P2(1)/m, with lattice dimensions of a = 11.909(2) angstrom, b = 21.174(4) angstrom, c = 11.983(2) angstrom, beta = 117.071(4)degrees, and V = 2690.6(8) angstrom(3), for delta = 0.35(2) (Z = 4). The structure contains corner-, edge-, and face-sharing CuTe4 tetrahedra interconnected with almost planar CuTe3 units. These connections result in a three-dimensional Cu atom network with numerous Cu-Cu bonds. With two Te-2(2-) dumbbells per formula unit, Ba3Cu14-delta Te12 is an electron-precise compound when delta = 0, according to (Ba2+)(3)(Cu+)(14)(Te-2(2-))(2)(Te2-)(8). For delta > 0, the materials are degenerate semiconductors with moderate Seebeck coefficients and electrical conductivities, in accord with the electronic structure calculations, and exhibit extremely low thermal conductivity.