5-Fold Rotational Symmetry - Practical Electron Microscopy and Database - - An Online Book - |
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Microanalysis | EM Book https://www.globalsino.com/EM/ | ||||||||
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Different from 4-fold and 6-fold rotational axes, two parallel 5-fold rotational axes cannot generate translational symmetry at the same distance of separation as in the original pair and thus no periodicity will result; therefore, they cannot coexist for 5-fold as shown in Figure 1458a. Figure 1458a. Two parallel 5-fold rotational axes which do not generate translational symmetry. In reality, not all rotational symmetries are allowed in crystals. The only rotational symmetries possible in crystal lattices are 2, 3, 4 and 6, because it is impossible to fill space with other symmetries (e.g. 5, 7 …). However, quasi-crystals, e.g. with 5-fold rotational symmetry, can be formed. Figure 1458b. Two-dimensional illustration of a quasi-crystal with 5-fold rotational symmetry. Note that the typical diffraction patterns of quasicrystals exhibit 5-fold or 10-fold rotational symmetry.
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