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Reduction in a niobium tungsten bronze, 2Nb 2 O 5 .7WO 3 , studied by 1 MV HRTEM
Author(s) -
Horiuchi S.
Publication year - 1982
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889882012059
Subject(s) - niobium , tungsten , high resolution transmission electron microscopy , bronze , materials science , reduction (mathematics) , metallurgy , crystallography , transmission electron microscopy , chemistry , nanotechnology , geometry , mathematics
1 MV high‐resolution transmission electron microscopy (HRTEM) reveals that the reduction in a niobium tungsten bronze, 2Nb 2 O 5 .7WO 3 , is initiated by the release of a small amount of oxygen from the – M –O– M –O– strings in the pentagonal tunnels. Its content can be measured from the weight change. At the second stage of reduction the ordered structure of 2Nb 2 O 5 .7WO 3 is destroyed, i.e. the ReO 3 ‐type structure at the center of the unit cell disappears. As a result an apparently disordered matrix appears, in which isolated unit cells of 2Nb 2 O 5 .7WO 3 and 4Nb 2 O 5 .9WO 3 are irregularly formed. At the third stage the microdomains of 4Nb 2 O 5 .9WO 3 appear and grow. The presence of oxygen vacancies in the strings at each stage is revealed by the technique utilizing the knock‐on of atoms by the impact of electrons. The number of knocked‐on atoms is analyzed with the help of computer simulation on image contrast. Circular diffuse scattering is excited from the disordered matrix and its origin is related to the clusters composed of nine tunnel sites.