Shear planes oxide structure

Non-stoichiometric oxides with high levels of disorder may adopt two modes of stabilization aggregation or elimination of point defects. Point defect aggregates forming clusters are examples of the former and extended defect structures like crystallographic shear-plane structures are examples of the latter. 

Perovskite Materials. Our studies of these materials are still in their infancy. An important feature of the perovskites is the ability to form many phases through shear planes where layers of a metal oxide can be inserted between multiple perovskite structure layers. Our work has shown that probe ions can be used to watch this process and we have been able to show that site selective laser spectroscopy is sensitive to all of the phases with a high sensitivity to even small concentrations. 

A further set of problems which obviously follows from the above discussion concerns the mechanism of shear-plane formation, although we should emphasize that the considerations involved here are quite separate from the thermodynamic ones discussed above. We discuss these mechanistic problems in Section 4 after considering a second structural feature in shear-plane systems, viz. the remarkable long-range ordering that commonly occurs in oxides containing these defects. 

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