Symmetry Determination

Abstract

In this chapter we describe the use of CBED patterns to determine the point and space group of a small crystal. Since this determination can be made from nanometer-sized regions of crystal, the method has proven extremely useful, in combination with X-ray microanalysis, for identifying microphases in multiphase materials, and for the study of the symmetry changes which accompany phase transitions (Ecob et al., 1981b). Review articles outlining the procedure can be found in Buxton et al. (1976), Eades et al. (1983), Goodman (1975), Tanaka (1989), and Steeds and Vincent (1983). The method requires one or more CBED patterns to be recorded at the highest-symmetry zone axes, including the outer HOLZ ring(s).