Thermoelectric Properties of the New Polytelluride Ba₃Cu_14-δTe₁₂

Ba 3 Cu 14 - δ Te 12 was prepared by directly reacting the elements in stoichiometric ratios at 800 °C for 3 days, followed by slow cooling. Ba 3 Cu 14 - δ Te 12 forms a new structure type, space group P 2 1 / m, with lattice dimensions of a = 11.909(2) Å, b = 21.174(4) Å, c = 11.983(2) Å, β = 117.071(4)°, and V = 2690.6(8) Å 3, for δ = 0.35(2) ( Z = 4). The structure contains corner-, edge-, and face-sharing CuTe 4 tetrahedra interconnected with almost planar CuTe 3 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, Ba 3 Cu 14 - δ Te 12 is an electron-precise compound when δ = 0, according to (Ba 2+ ) 3 (Cu + ) 14 (Te 2 2 - ) 2 (Te 2 - ) 8 . For δ > 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.