Misfit defects

Erom the preceding discussion, the distinction between misfit defects shear domains formed by pure shear and CS planes formed by the elimination of anion vacancies in a specific crystallographic plane by shear and the collapse of the oxide lattice on that plane can be understood. This distinction between defects is central to catalytic reaction mechanisms in oxides. However, it is often not made in the literature on oxide catalysis and solid state oxide chemistry. This can result in an incorrect interpretation of observed data and of the role played by lattice oxygen atoms in catalytic reactions. The former are regions containing... 

On M0O3, methanol (CH3OH or MeOH) chemisorbs at a low temperature of 100°C, which suggests that some defects (or dangling bonds) are necessary for chemisorption. In situ ETEM experiments in methanol show the formation of misfit defects at 100°C (and surface domains) accommodating the shape... 

It should be pointed out that positrons can also be trapped by misfit defects at the matrix-precipitate interface or by defects inside a precipitate, despite the positron s affinity for the precipitate. 

Extended defects range from well characterized dislocations to grain boundaries, interfaces, stacking faults, etch pits, D-defects, misfit dislocations (common in epitaxial growth), blisters induced by H or He implantation etc. Microscopic studies of such defects are very difficult, and crystal growers use years of experience and trial-and-error teclmiques to avoid or control them. Some extended defects can change in unpredictable ways upon heat treatments. Others become gettering centres for transition metals, a phenomenon which can be desirable or not, but is always difficult to control. Extended defects are sometimes cleverly used. For example, the smart-cut process relies on the controlled implantation of H followed by heat treatments to create blisters. This allows a thin layer of clean material to be lifted from a bulk wafer [261. 

Fig. 21. (a) The nature of the glide shear plane defects in three-dimensional projection and (b) in one layer of idealized structure, showing the novel glide shear process and the formation of glide shear plane defects. Filled circles are anion vacancies, (c) Schematic of glide shear. Glide defects accommodate the misfit at the interface between catalyst surface layers with anion vacancies (filled circles) and the underlying bulk (85,89). 

Fig. 22. ETEM at 180°C in N2, illustrating the stability of gold nanorods, for nanoelectronics and catalysis applications. Gold atomic layers and surface atomic structures are visible. Surface of gold nanorod at room temperature showing twin defect lamellae on the atomic scale. They indicate interaction of the surfactant with the (110) surface forming twins to accommodate the shape misfit between the two.

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