(3 + 2)-Dimensional superspace approach to the structure of the stage-2 misfit layer compound (SbS)1.15(TiS2)2

Abstract

The inorganic misfit layer compound (SbS)1.15(TiS2)2 was prepared by high-temperature reaction of the elements. It can be regarded as a stage-2 phase intercalation compound where double layers of SbS are inserted into the van der Waals gaps of TiS2 with stacking sequence ...[TiS2][SbS][TiS2][TiS2][SbS][TiS2].... The structure, determined by single crystal X-ray diffraction on the basis of the (3 + 2)-dimensional superspace group C{\bar 1}, is described by two interpenetrating, incommensurately modulated subsystems. The first subsystem comprises double sandwiches of TiS2 with 1T-TiS2 structure. The lattice parameters are a 11 = 3.404 (1), a 12 = 5.908 (3), a 13 = 17.068 (3) Å, α 1 = 86.28 (2), β 1 = 96.40 (2) and γ 1 = 90.00 (2)°. The second subsystem is built of intrinsically interface modulated double layers of SbS. Unit-cell dimensions of the basic structure are given by a 21 = 2.950 (1), a 22 = 5.932 (2), a 23 = 17.008 (2) Å, α 2 = 85.82 (1), β 2 = 85.30 (1), γ 2 = 84.11 (1)°. The interface modulation wavevector of SbS is given by q = 0.411 (2)a*21 + 0.822 (4)a*22. The two subsystems have the common (a* v2, a* v3) plane. Refinement on 3112 reflections with I > 2.5σ(I) converged to R = 0.088 (wR = 0.108). The structure consists of both occupational and displacive modulations for the atoms in the SbS subsystem. The SbS subsystem has the same structural features as found in the compound (SbS)1.15TiS2 [Ren, Meetsma, Petricek, van Smaalen & Wiegers (1995), Acta Cryst. B51, 275–287]. But stacking disorder of SbS is found corresponding to displacements of the layers along the a 21 axis; the final structure model involves a rigid shift of 0.63 (2) Å of 5.5 (4)% of SbS to both sides along a 21.