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Twinning: Difference between revisions
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→'''Warning Signs for Twinning'''
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c) If different crystals of the same compound show significantly different Rint values for the higher symmetry Laue group, this clearly shows that the lower symmetry Laue group is correct and indicates different extents of twinning. | c) If different crystals of the same compound show significantly different Rint values for the higher symmetry Laue group, this clearly shows that the lower symmetry Laue group is correct and indicates different extents of twinning. | ||
d) The mean value for |E^2-1| is much lower than the expected value of 0.736 for the non-centrosymmetric case. If we have two twin domains and every reflection has contributions from both, it is unlikely that both contributions will have very high or that both will have very low intensities, so the combined intensities are distributed to give fewer extreme values. | d) The mean value for |E^2-1| is much lower than the expected value of 0.736 for the non-centrosymmetric case (see also [[Intensity statistics]]). If we have two twin domains and every reflection has contributions from both, it is unlikely that both contributions will have very high or that both will have very low intensities, so the combined intensities are distributed to give fewer extreme values. | ||
e) The space group appears to be trigonal or hexagonal. | e) The space group appears to be trigonal or hexagonal. | ||