Crystal growth of uranium-containing complex oxides: Ba_2Na_(0.83)U_(1.17)O_6, BaK_4U_3O_(12) and Na_3Ca_(1.5)UO_6

摘要

Single crystals of complex uranium oxides, Ba_2Na_(0.83)U_(1.17)O_6 , BaK_4U_3O_(12) and Na_3Ca_(1.5)UO_6, were grown out of reactive carbonate melts. The crystal structures the three uranates were determined by single crystal X-ray diffraction. Ba_2Na_(0.83)U_(1.17)O_6 crystallizes in the Fm3m space group, a = 8.6173(1), with a disordered cubic double perovskite structure. BaK_4U_3O_(12) forms in the cubic lm3m 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_(1.5)UO_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 U06 octahedra in Ba2Nao.s3U1.17O6 are undistorted due to oxygen disorder, the UO_6 octahedra in BaK_4U_3O_(12) and Na_3Ca_(1.5)UO_6 feature the typical uranyl geometry with four long two short U-O bonds.