Determination of the incommensurately modulated structure of Cu3-xTe2

The incommensurately modulated structure of copper telluride Cu3-xTe2 (Cu2.91Te2) with modulation wavevector q=0.397(1)a*+1/2c* has been determined by X-ray diffraction at room temperature (974 unique reflections). The lattice parameters of the primitive orthorhombic cell of the average structure are: a=3.9727(4), b=4.0020(5), c=6.1066(3) A, V=97.1 A3, Z=2, μ=304 cm-1 (λ=0.7107 A), Mr=440.1. The symmetry of the structure is given by the superspace group Csub(anti 1 1 1)Pmmn. The final RF factor is 0.045. The modulated structure is related to the structure of Ni3±xTe2 and, as in the latter compound, the occupation of the octahedral sites by metal atoms varies throughout the range 0 to 1. Different from the nickel telluride structure is the antiphase ordering along c together with a different displacement pattern of the atoms, which can be ascribed to a different interaction strength and a different charge transfer between the metal atom and Te. (orig.)