Abstract
A series of monophosphate tungsten bronzes of composition P 4O 8(WO 3) 2 m with pentagonal tunnels, MPTB P, have been investigated by high resolution electron microscopy. Most of the micrographs of the integral m members exhibit an asymmetrical contrast which could not be explained qualitatively by the structural models derived from X-ray diffraction studies of some members of the series. Image calculations were thus performed on the m = 4 member (P 4W 8O 32), which showed that the unexpected symmetry does not result from a structural anomaly, but could be due to a titled electron beam. The observations revealed that ordered crystals can be obtained up to m = 16. The investigation of the nonintegral m compositions showed two sorts of intergrowths: disordered intergrowths of different m members belonging to the MPTB P series and ordered intergrowths of the MPTB P structure with a related phosphate tungsten bronze structure based upon hexagonal tunnels.
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