Calidris

Space Group Determinator


An electron precession pattern of the cubic mineral mayenite, along [011], to be processed by ELD.

The reflections in the Zero Order Laue Zone (ZOLZ) (insiode the red circle) are first found and integrated, resulting in a lattice. Then the First Order Laue Zone (FOLZ) are found (between the red and green circles, Space Group Determinator notices that the two lattices are shifted relative each other a sure sign of centered lattice.

The symmetry is determined, individually for the ZOLZ and HOLZ regions. Often the symmetry is lower for the HOLZ, but in this case both ZOLZ and HOLZ have 2mm symmetry. This is compatible with many possible crystal classes, as seen in the table to the right in the figure above.

Finally also the extinction conditions are taking into account. Then only a very small selection of possible crystal classes and zone axes are possible. Another example:

Precession electron diffraction pattern of Mayenite along [111]

Finally, the Mayenite_111 pattern is analysed:

Here the symmetry is 6mm in the ZOLZ but only 3m1 in the FOLZ. This excludes tetragonal and hexagonal, but allows trigonal. The systematic absences are only compatible with rhomohedral (in hexagonal setting) [001] and I-centered cubic.
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