Crystal growth of uranium-containing complex oxides: Ba 2Na 0.83U 1.17O 6, BaK 4U 3O 12 and Na 3Ca 1.5UO 6

Abstract

Single crystals of complex uranium oxides, Ba 2Na 0.83U 1.17O 6, BaK 4U 3O 12 and Na 3Ca 1.5UO 6, were grown out of reactive carbonate melts. The crystal structures the three uranates were determined by single crystal X-ray diffraction. Ba 2Na 0.83U 1.17O 6 crystallizes in the F m 3 ¯ m space group, a = 8.6173(1), with a disordered cubic double perovskite structure. BaK 4U 3O 12 forms in the cubic I m 3 ¯ 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. Na 3Ca 1.5UO 6 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 UO 6 octahedra in Ba 2Na 0.83U 1.17O 6 are undistorted due to oxygen disorder, the UO 6 octahedra in BaK 4U 3O 12 and Na 3Ca 1.5UO 6 feature the typical uranyl geometry with four long two short U–O bonds.