HREM studies of complex uranium oxides containing molybdenum and tungsten

Crystal Structures of U(Ta,W)5O16and U(Ta,W)2O8Revealed by High-Resolution Transmission Electron Microscopy

“…It should be mentioned that ReO -type slabs with n' 3 have not yet been observed in the U(Ta,W) O crystals. The above results are in analogy with previous observations that substitution of tungsten for molybdenum increases the width of the ReO -type slabs both in complex U-Mo-W oxides (13) …”

“…2c can be described as built up of ReO -type slabs of tilted octahedra, two (Ta,W)O -octahedra wide (n"2), which are intergrown with thin slabs of edge-sharing pentagonal UO bipyramids (PB). This type of structure has previously been denoted (2)-PB (13). From the SAED pattern (Fig.…”

“…No ordered fragment or large region of the (3)-HB type structure has been observed so far in the system. A phase of this structure type, U Mo W O , with half occupancy of the uranium positions has been reported, however (13).…”

Ordered and Defect Structures in the UO2–WO3System, Revealed by HREM

“…This study has been supported by the Swedish Natural oxides with the general formula UO и M n O 3nϩ1 , where Science Research Council. M ϭ Mo, W and n corresponds to the number of octahedra across the ReO 3 -type slab (1). As the structures…”

“…Another orthorhombic phase, Several phases in the system UO 2 -MoO 2 -MoO 3 -WO 3 U 5 W 19 O 67 , assumed to be structurally related to U 3 O 8 , has have been prepared and studied by high-resolution elec-also been observed (8). tron microscopy (HREM) combined with X-ray powder and single-crystal diffraction (1)(2)(3). The phases observed EXPERIMENTAL were either oxides containing uranium and molybdenum or uranium, molybdenum, and tungsten.…”