Acta Crystallographica Section B

Structural Science

Volume 52, Part 3 (June 1996)

research papers

Acta Cryst. (1996). B52, 389-397 [ doi:10.1107/S0108768195014248 ]

(3 + 2)-Dimensional superspace approach to the structure of the stage-2 misfit layer compound (SbS)_1.15(TiS₂)₂

Y. Ren, A. Meetsma, G. A. Wiegers and S. van Smaalen

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 a₁₁ = 3.404 (1), a₁₂ = 5.908 (3), a₁₃ = 17.068 (3) Å, ₁ = 86.28 (2), ₁ = 96.40 (2) and 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 a₂₁ = 2.950 (1), a₂₂ = 5.932 (2), a₂₃ = 17.008 (2) Å, ₂ = 85.82 (1), ₂ = 85.30 (1), 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 > 2.5(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 a₂₁ axis; the final structure model involves a rigid shift of 0.63 (2) Å of 5.5 (4)% of SbS to both sides along a₂₁.