Determination of the incommensurately modulated structure of Ni_3±<i>x</i>Te₂

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), 6.084 (4) angstrom with V = 86.9 angstrom3, Z = 2, mu = 317 cm-1 (lambda = 0.7107 angstrom), M(r) = 416.4. The symmetry of the structure is given by the superspace group P11sBAR(Pmmn) Unlike the analogous Cu compound [Schutte &amp; de Boer (1993). Acta Cryst. B49, 398-403] there is no antiphase ordering along c. The final R(F) 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 (p(NiII) varying between 0 and 1). The Ni and Te atoms are slightly displaced, incommensurately with the basic lattice.