Crystal growth of uranium-containing complex oxides: Ba2Na0.83U1.17O6, BaK4U3O12 and Na3Ca1.5UO6

Single crystals of complex uranium oxides, Ba2Na0.83U1.17O6, BaK4U3O12 and Na3Ca1.5UO6, were grown out of reactive carbonate melts. The crystal structures the three uranates were determined by single crystal X-ray diffraction. Ba2Na0.83U1.17O6 crystallizes in the Fm3¯m space group, a = 8.6173(1), with a disordered cubic double perovskite structure. BaK4U3O12 forms in the cubic Im3¯m space group, a = 8.7232(1), with the asymmetric unit consisting of three metal positions, which shows improvement of the structure refinement from the published results. Na3Ca1.5UO6 crystallizes in the orthorhombic Fddd space group with a = 6.6573(2), b = 9.6111(3) and c = 20.1155(5) in a rock salt superstructure. In all three oxides the U(VI) cation is octahedrally coordinated. While the UO6 octahedra in Ba2Na0.83U1.17O6 are undistorted due to oxygen disorder, the UO6 octahedra in BaK4U3O12 and Na3Ca1.5UO6 feature the typical uranyl geometry with four long two short U–O bonds.

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