Structure of UMoO₅ studied by single-crystal X-ray diffraction and high-resolution transmission electron microscopy

A combination of X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) has been used to study the crystal structure of molybdenum uranium pentoxide, UMoO₅, obtained by hydrothermal and ceramic methods. Crystal data: M_r = 414.0, orthorhombic, Pbaa (number 54), a = 12.746 (1), b = 7.3494 (7), c = 4.1252 (2) Å, V = 386.4 (1) Å³, Z = 4, D_x = 7.116 Mg m^-3, R = 0.037 for 723 reflections. The structure of UMoO₅ is related to that of UVO₅. Both are built up by slabs of pentagonal UO₇ bipyramids with slabs of MO₆ octahedra in-between. They differ in symmetry due to different types of displacement of the M atoms from the ab plane. The HRTEM study revealed a few defect regions in the UMoO₅ crystals prepared by ceramic methods. Energy-dispersive spectroscopy (EDS) analyses indicate a slight excess of uranium in such crystals. Hypothetical models of defect regions are given.

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