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Synthesis and Structural Analysis of Sr5.8La4.4Ti7.8S24O4 and La14Ti8S33O4:  Two New Oxysulfides Containing a Common [(Ti4S2O4)(TiS6)4/2]12- Layer

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journal contribution
posted on 12.09.1996, 00:00 by Louis J. Tranchitella, James C. Fettinger, Bryan W. Eichhorn
Two new titanium oxysulfides Sr5.8La4.4Ti7.8S24O4 and La14Ti8S33O4 were prepared by high-temperature methods (925−950 °C; ∼ 90−104 h) from stoichiometric ratios of SrS, La2S3, Ti, S, and TiO2 or La2O3 (or SrO for Sr5.8La4.4Ti7.8S24O4) oxygen sources. The sample crystallinity and purity was greatly enhanced when LaCl3 fluxes were employed. The compounds were characterized by single-crystal and powder (Rietveld profile analysis) X-ray diffraction studies and EDX analysis. Both compounds are black insulators (all Ti4+) and contain a common [(Ti4S2O4)(TiS6)4/2]-12 layer despite the difference in composition and crystal symmetry. For La14Ti8S33O4, these layers are separated by TiS6 octahedra and 8- and 9-coordinate La−S polyhedra. For Sr5.8La4.4Ti7.8S24O4, the layers are separated by a TiS6 octahedron and two disordered Ti1-xSrxS6 octahedra. La and Sr are also disordered on an interlayer nine-coordinate site. Crystal data (153 K):  Sr5.8La4.4Ti7.8S24O4, tetragonal, space group P4/mmm a = 10.569(3), c = 8.516(4) Å, V = 951.4(5) Å3, Z = 1, R(F) = 4.28%, and Rw(F2) = 10.39%. For La14Ti8S33O4, monoclinic, space group C2/m, a = 14.904(1) , b = 14.736(1), c = 12.278(1) Å, β = 112.773(5)°, V = 2486.2(3) Å3, Z = 2, R(F) = 3.92%, and Rw(F2) = 10.00%.