Electron microscopy
 
Tetragonal Space Groups
- Practical Electron Microscopy and Database -
- An Online Book -
Microanalysis | EM Book                                                                                   http://www.globalsino.com/EM/        

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The tetragonal space groups may be classfied into two groups, i.e. with and without additional symmetry with respect to the x and y axes. In the names of tetragonal space groups, the first letter denotes the lattice type and the second letter indicates the four-fold symmetry that is always chosen to align parallel to the z axis. For those space groups with symmetry along other axes, the next part of the name indicates the symmetry with respect to both the x and y axes, while the remaining part indicates the symmetry with respect to both of the diagonals between the x and y axes.

For the enlarged tetragonal unit cells, i.e. C or F centred unit cells, the symbols selected to describe the symmetry with respect to the x and y axes, and with respect to the face-diagonal directions is simply the same as that selected for the equivalent P and I centred cells, but with the order of the symbols reversed e.g. the name C4/mmb is used for the enlarged unit cell of space group P4/mbm.

 

 

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