STUDY OF THE IRON-NITROGEN PHASES BY ELECTRON MICRODIFFRACTION AND CONVERGENT-BEAM ELECTRON-DIFFRACTION

It is shown how electron microdiffraction connected with convergent beam electron diffraction can be used to identify unambiguously the space group of the gamma, gamma' and epsilon iron nitrides. The method involves the identification, from microdiffraction patterns, of a partial extinction symbol in agreement with a few possible space groups. The actual space group is then identified by means of the Tanaka ''multibeam'' method or from observation of the intensity of the diffracted beams on microdiffraction patterns. It is explained how to overcome the experimental difficulties connected with the small crystal size, the texture of the specimen and the absence of HOLZ reflections on most diffraction patterns.