Convergent beam electron diffraction and the determination of crystal symmetry

The experimental technique of electron microdiffraction using a focussed convergent electron probe is reviewed, and the form and origin of convergent beam electron diffraction (CBED) patterns described. Applications to (a) structural analysis with high spatial resolution, (b) crystal symmetry determination (including the identification of crystal space group), and (c) detection of small local changes in crystal lattice dimensions or symmetry are discussed. The improved spatial resolution and three-dimensional crystallographic information obtained are emphasized. An example is presented of application to determination of the crystal symmetry of the oxide Y//2O//3 dispersed in yttrium.