SYNTHESIS, HIGH-RESOLUTION ELECTRON-MICROSCOPY AND CRYSTAL-STRUCTURE REFINEMENT OF THE CLUSTER COMPOUND BA3NB16O23 BY X-RAY AND NEUTRON-DIFFRACTION

• Ba3Nb16O23 was prepared by reducing a mixture of BaCO3 and Nb2O5 with acetylene soot under vacuum at 1550-1600-degrees-C. The structure was determined from high resolution electron microscopy images and was refined by the Rietveld technique using X-ray and neutron powder diffraction data. The unit cell parameters are a = 20.9301(4) angstrom, b = 12.4785(3) angstrom and c = 4.1619(1) angstrom, space group Cmmm, Z = 2. The crystal structure can be described as an intergrowth of BaNbO3 and NbO. Characteristic building units are quadruple chains of corner-sharing Nb6 octahedra connected via columns with a perovskite-type structure to form a three-dimensional network.

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