収束電子回折法による４次元空間群の決定

Abstract

The interrelation between the symmetries of CBED patterns and symmetry symbols for incommensurately-modulated structures given by de Wolff, Jannsen and Janner are clarified. 1) Point groups; The symmetry symbol 1 shows no symmetry in CBED patterns. The symbols other than 1 show the symmetries of the corresponding symbols for the average structure. 2) Space groups; The four dimensional glide planes and screw axes give dynamical extinction in the kinematically forbidden reflections due to the symmetry elements. Dynamical extinction rules in CBED patterns were tabulated for one example of the four dimensional space groups.