Precipitation phenomena in non-stoichiometric oxides I. Pairs of crystallographic shear planes in reduced rutiles

High-resolution electron microscopy, in conjunction with controlled specimen preparation procedures, has enabled the nature and structure of the small defects existing within the nonstoichiometric phase TiO2-x (0 ≤ x ≤ 0.01) to be investigated. In particular, the precipitation of pairs of crystallographic shear planes (c. s. p.) and their subsequent separation has been observed. The atomic mechanisms involved in c. s. p. nucleation and growth and the eventual evolution to an ordered c. s. structure have been elucidated by using new linear cationic interstitial defect structural models. The results emphasize the decisive influence that cooling history has on the microstructures observed at room temperature and suggest that similar new phenomena will be discovered in observations of other non-stoichiometric chemical systems.