Precipitation phenomena in non-stoichiometric oxides II. {100} Platelet defects in reduced rutiles

High-resolution electron microscopy, in conjunction with controlled specimen preparation procedures, has enabled the nature and structure of novel {100} platelet defects found in TiO2-x (0 < x < 0.0035) to be studied at close to atomic resolution The precipitation of these platelet defects, often occurring in association with crystallographic shear planes (c.s.p.), can be explained in terms of new linear cationic interstitial defect models which must exist within the non-stoichiometric phase TiO2-x. Moreover, models for the platelet defects and c.s.p.-platelet defect structures have been derived that explain the topological features of the experimental images as well as shedding new light on the atomic mechanisms involved in precipitation of c.s.p. and platelets. The decisive influence that cooling history plays in determining the microstructures observed at room temperature in non-stoichiometric chemical systems is again emphasized. Finally, consideration of the elastic energy associated with torsional strains required to rotate [TiO6] octahedral chains of rutile in the vicinity of the platelet defects and the c.s.p. leads to a qualitative physical explanation for the changeover in precipitation structures from c.s.p. to platelets, dependent on temperature of precipitation (i.e. cooling rate).