Electron microscopy and diffraction of modulated structures
It is the purpose of this review to illustrate the possibilities of elect— ron microscopy and electron diffraction techniques for the study of modul— ated structures. A classification of these structures according to the type of modulating structural deviation is proposed. Some particular procedures are outlined for electron diffraction as well as transmission electron microscopy observations. Also the use of the structure imaging mode is discussed since it provides detailed information on the modulation type. Two particular examples are treated in some more detail since each illustrates particular applications of the above mentioned technioues: the charge density wave related phases in tantalum disulphide and an incommensurate intermediate phase near the a—n— transition in quartz.