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

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Different from unequivocal space groups, for equivocal space groups, there are several space groups possible for one set of systematic forbidden reflections. For instance, the three space groups C2/m, C2 and Cm have the same systematic forbidden reflections which are caused by the C-centering (h+k = 2n+1). The other symmetry operations in the three space groups, e.g. 2-fold rotation axis (2) and mirror plane (m) in the C2/m space group, do not cause forbidden reflections. In this case, each space group can only be distinguished by structure solution and refinement.

 

 

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