Crystal structure determination of the TiSe₂-based misfit layer compound (LaSe)_1.20(TiSe₂)₂

Abstract

Abstract The new inorganic misfit layer compound (LaSe) 1.20 (TiSe 2 ) 2 was prepared by high-temperature reaction of the elements. It can be regarded as an intercalate of TiSe 2 with LaSe double layers inserted into every second van der Waals gap of the TiSe 2 sandwiches (stage-2 intercalate). The structure, determined by single crystal X-ray diffraction on the basis of (3 + 1)-dimensional superspace, is described by two interpenetrating, incommensurately modulated subsystems. The first subsystem comprises of paired TiSe 2 sandwiches. Its basic space group is C [unk](0.5957(4), −0.0004(10), −0.189(4)) and the lattice parameters are a 11 = 3.556(2) Å, a 12 = 6.120(2) Å, a 13 = 17.876(10) Å, α 1 = 86.71(3)°, β 1 = 92.93(3)°, and γ 1 = 90.03(3)°. The second subsystem comprises of LaSe double layers with basic space group C [unk](1.679(1), 0.001(2), 0.317(6)) and unit cell dimensions a 21 = 5.969(2) Å, a 22 = 6.118(2) Å, a 23 = 17.859(9) Å, α 2 = 86.69(3)°, β 2 = 89.33(4)°, and γ 2 = 90.01(3)°. The two subsystems have the common ([unk],[unk]) plane. Refinement on 1602 reflections with I > 2.5 σ ( I ) converged to R = 0.126 ( wR = 0.155) for the average structure. Stacking disorder of TiSe 2 is found corresponding to displacements of the sandwiches along the [unk] 21 axis; in the final structure model 9.9(4)% of TiSe 2 is rigidly shifted by ½ [unk] 11 .