Point Defects in Nb22O54 Oxidized at 200°C

Abstract
The structural changes in a Nb22O54 crystal heated at 200°C in air were examined using 1 MV high-resolution transmission electron microscopy. At the initial stage of oxidation, NbO6 octahedra are locally shifted by one atomic distance. This movement induces two types of point defect, which array in a string of limited length. Both require additional oxygen atoms at the interstitial sites and, therefore, can act as a possible mechanism for oxidation. At the advanced stage of oxidation, a superstructure is formed.