Electron microscopy
Projection-Diffraction Symmetry
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Projection-diffraction symmetry [1] corresponds to the symmetry of the diffraction disks and diffuse intensity within diffraction disks of the zero-order Laue zone (ZOLZ) symmetry, which excludes the HOLZ lines in the bright field disks.

Figure 1601 shows the projection-diffraction symmetry of the [0001] CBED pattern of T1 (Al2CuLi) crystals. The pattern symmetry is 6mm.

[0001] CBED patterns of T1 (Al2CuLi) crystals: Projection-Diffraction Symmetry
Figure 1601. Projection-diffraction symmetry of the [0001] CBED pattern of T1 (Al2CuLi) crystals. Adapted from [2]

Note that the projection-diffraction symmetry can never be lower than the whole-pattern symmetry since the whole-pattern symmetry reflects the symmetry of the full three-dimensional (3-D) crystal.






[1] B. E Buxton, J.A. Eades, J.W. Steeds, and G.M. Rackham: Phil. Trans. Roy. Soc., vol. 281, A1301, pp. 171-94.
[2] Kenneth S. Vecchio and David B. WILLIAMS, Convergent Beam Electron Diffraction Analysis of the T1 (Al2CuLi) Phase in Al-Li-Cu Alloys, Metallurgical Transactions A, 19A, 1988-2885, (1988).