Etude précise des diagrammes de diffraction électronique de poudres de cristaux à grands paramètres. Exemple des phosphates de calcium. Intérêt de la diffraction à très haute tension. Calcul et tracé de diagrammes théoriques

A simple and universal technique is described for the preparation of dry powder specimens for transmission electron diffraction and microscopy. An elaborate study of the obtainment and the interpretation of Debye-Scherrer electron diffraction patterns is presented, with particular attention to matters which determine the possibility of identifying substances with low crystal symmetry or large parameters: the observation of rings near the center of the pattern, the accuracy of the measurements of interplanar spacings, the resolving power, the contrast. It appears that voltages of some hundreds of kilovolts are generally the most appropriate for rapid electron diffraction. A method is given for computing and drawing with sufficient accuracy theoretical Debye-Scherrer patterns of substances with complex crystalline structure.