Interpreting HRTEM Images

Here is a HTEM picture of grain boundaries in BaTiO3, one of the most important electroceramic materials. Its lattice is of the Perovskite type and looks like this:
 
Perovskite lattice
 
The Ti atom is in the center and the O atoms on the face centers positions. The lattice is not exactly cubic but slightly elongated. A HRTEM image from Prof. Urbans group (Res. Center Jülich) shows many grain boundaries:
 
HRTEM of BaTiO3
 
The link provides a large-size copy. Can you figure out the structure of the boundaries? Are there any dislocations present? This is not so much an exercise but a demonstration that even images with atomic resolution do not solve all problems.
 

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go to Ionic Crystals

go to 8.3.1 Steps in Interfaces

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