APPLICATION OF MICRODIFFRACTION TO CRYSTAL-STRUCTURE IDENTIFICATION

In a previous paper by J.P. Morniroli and J.W. Steeds [Ultramicroscopy 45 (1992) 219] it was shown that microdiffraction patterns obtained w ith a nearly parallel electron beam and a small spot size can be used to identify and to characterize crystal structures. A systematic metho d was proposed to deduce, via the Buerger extinction symbol, the space group or a set of consistent space groups. In order to illustrate how this method can be applied experimentally, three examples concerning the sigma, chi and R intermetallic phases are detailed. Experimental s olutions are given to overcome difficulties connected with the frequen t absence of high-order Laue zone reflections on high-symmetry zone ax is patterns. The possibility to identify the Buerger extinction symbol from a unique zone axis pattern is also explored.