Determination of the incommensurately modulated structure of Ni3±xTe2

The modulated structure of nickel telluride Ni3±xTe2 (Ni2.76Te2) is stabilized at 300 K by the substitution of a small amount of Fe (prepared as Ni2.57Fe0.29Te2). The structure of this compound has been determined by X-ray diffraction at room temperature (1311 unique reflections). The structure is incommensurately modulated with wavevector q=0.378(1)a*. The lattice parameters of the primitive orthorhombic cell of the average structure are: a=3.761(1), b=3.796(1), c=6.084(4) A with V=86.9 A3, Z=2, μ=317 cm-1 (λ=0.7107 A), Mr=416.4. The symmetry of the structure is given by the superspace group Psub(anti 1 1 s)Pmmn. Unlike the analogous Cu compound there is no antiphase ordering along c. The final RF factor is 0.047. Both occupational and displacive modulation functions are needed to describe the structure. The occupation of the distorted octahedral sites by Ni atoms is fully modulated (PNiII varying between 0 and 1). The Ni and Te atoms are slightly displaced, incommensurately with the basic lattice. (orig.)