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

It is shown how electron microdiffraction connected with convergent be am electron diffraction can be used to identify unambiguously the spac e group of the gamma, gamma' and epsilon iron nitrides. The method inv olves 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 ''multibe am'' method or from observation of the intensity of the diffracted bea ms on microdiffraction patterns. It is explained how to overcome the e xperimental difficulties connected with the small crystal size, the te xture of the specimen and the absence of HOLZ reflections on most diff raction patterns.