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In-situ Oxidation Products of Nb4W13O47: A High-Resolution Transmission Electron Microscopy Study

✍ Scribed by F. Krumeich; J. L. Hutchison; M. J. Sayagués

Publisher
John Wiley and Sons
Year
1999
Tongue
German
Weight
815 KB
Volume
625
Category
Article
ISSN
0372-7874

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✦ Synopsis

Crystallites of Nb 4 W 13 O 47 were heated by a focussed electron beam in an oxygen atmosphere (p O 2 = 20 mbar) inside the gas reaction cell installed within the polepiece of a 400 kilovolt transmission electron microscope. The HRTEM investigation of the resulting oxidation products revealed the presence of structures which differ significantly from those generated by conventional oxidation in air. In a first reaction step, the arrangement of filled pentagonal tunnels in the tetragonal tungsten bronze (TTB) substructure became disordered, and small segregations of ReO 3 -type structure arose. Further treatment largely destroyed the original TTB-type structure. In the residual bronze-type structure, only a few TTB subcells were pre-served while unusual structural arrangements, including hexagonal and heptagonal tunnels, were formed. Moreover, microdomains of a new intergrowth structure between the TTB type and the ReO 3 type occur. This structure comprises double pentagons of octahedra as well as slabs of diamondlinked pentagonal columns. The oxygen excess in the oxidation product is structurally accommodated in large ReO 3type domains of tungsten oxide.

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