Etude des profils des bandes de diffraction X d'une beidellite-Na hydratée à deux couches d'eau. Détermination du mode d'empilement des feuillets et des sites occupés par l'eau

Intensities and shapes of the (02,11), (20,13) and (04, 22) diffraction bands are calculated for model structures and are fitted to the experimental patterns, in order to describe the structural characteristics of a two-water-layer Na-beidellite (Rupsroth, Bavaria, Germany). The determined features are: the average dimensions and size distributions of coherent domains, the coordinates of the crystallographically bound water molecules, the nature and abundance of stacking defects. The localization of the water sites and the determination of their occupancy rates are obtained using a general and powerful procedure which is described. For the stacking, a quantification of the influence, on the X-ray powder diagrams, of all crystallochemically possible modes given in the literature has been done. On the basis of such a quantification, it was possible to establish the layer succession law in the studied hydrated particles.