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Abstract---X-ray diffraction (XRD) characterization of natural and intercalated smectites is usually limited to the apparent d-value estimated from the peak maxima in the raw data. This can lead to the misinterpretation of the measured data. In the case of XRD, the interference function is modulated by instrumental factors (Lorentz-polarization factor, diffraction geometry) and physical factors (structure factor, surface roughness effect). These effects lead to diffraction profile distortions, depending on the diffraction angle and peak full width at half maximum (FWHM). As a result, the diffraction profiles for structures with large line broadening (FWHM > 1 ~ exhibit a significant peak shift (Ad --1.5 A), especially at low angles (20 --< 10~ The present work deals with the detailed analysis of all these effects, their corrections and their consequences for the interpretation of diffraction patterns (including possible errors in determining lattice parameters or the structure model). The investigated materials were montmorillonites (MMT) intercalated with hydroxy-A1 polymers. Diffraction profile analysis revealed the corrected d-values and showed that the intercalated sample is not a mixed-layered structure. As a result a structural model of the interlayer is presented.

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Molecular simulations using the Cerius2 modelling environment have been used to investigate the structure of montmorillonite (MMT) intercalated with Zn cations. Basal spacing and bonding of Zn2+ cations in the interlayer have been investigated with regard to their dependence on the water content. In the first part of the work, Zn cations in the interlayer are coordined by six water molecules and the energy of the system is discussed. The energy discussion is focused on the influence of the different starting orientations of the Zn octahedron, and different positions of Mg atoms in the octahedral sheet. An energy scan at fixed d-spacing was carried out. Later the hydration simulation giving the hydration curve (i.e. the dependence of d-spacing on the number of water molecules in the interlayer) was also carried out. Two different hydration states were found — for certain humidity ranges there is almost constant d-spacing and between these intervals there is a sharp edge. Finally the structure of totally dehydrated Zn-MMT was simulated.

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