Crystal chemistry of the BaNbS system: A layer structure of approximate composition Ba2NbS4(S2)0.5 |
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Authors: | JS Swinnea H Steinfink LERendón-Diaz Mirón L Banos-López |
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Institution: | Department of Chemical Engineering, Materials Science and Engineering Laboratories, The University of Texas, Austin, Texas 78712 USA;Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma, Apdo. Postal 70-360, Mexico, D.F., Mexico |
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Abstract: | Black platy crystals from the product of a reaction mixture of 6BaS : 3Nb : 7S reacted at 1000°C were hexagonal with a = 6.909(4) Å, c = 49.25(2) Å, . A pronounced subcell with a = 6.91Å, c = 5.5 Å indicated that this was a layer structure consisting of stacking of close-packed BaS3 layers. Three dimensional X-ray diffraction data were collected from a single crystal using monochromatized MoKα radiation. From the 1535 measured reflections, 782 unique structure amplitudes were obtained of which 608 greater than 2σ(F) were used to solve the structure. The final R = 0.1065, ωR = 0.0793; for 91 reflections with l = 9n, R = 0.0397 and for the 517 reflections l ≠ 9n, R = 0.138. The structure is based on the stacking of close-packed BaS3 layers with the sequence CBDBABDBC BCDCACDCB, where D designates a disordered layer. The disordered layers contain two crystallographically independent Ba with partial site occupancies and disordered S2 and S ions. Nb occupy octahedral interstices and form two different arrangements; a unit consisting of 3 face-sharing octahedra and a unit of 2 face-sharing octahedra. These octahedral units are separated by the disordered layers. The NbNb distances in the chain of 3 are 3.29 Å and they are 3.57 Å in the double unit. |
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