Trigonal & Rhombohedral Space Groups  Practical Electron Microscopy and Database   An Online Book  

Microanalysis  EM Book https://www.globalsino.com/EM/  


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In the names of trigonal and rhombohedral space groups, the first symbol denotes the lattice type, and the second symbol denotes the threefold symmetry that is always selected to lie parallel to the z axis. Additional symmetry elements may be parallel to the x and y axes (e.g. the twofold rotation axes in P321) or perpendicular to them (e.g. the twofold rotation axes in P312). The order of the last two symbols in the space group names is used to distinguish the two possibilities. In the names of hexagonal space groups, the order of the symbols is similar to that of the trigonal space group symbols except that the symmetry with respect to the z axis is sixfold.


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